Introduction

Boron, with an electronegativity of 2.0, has endued corresponding boronic acids and their esters to be one kind of useful functional groups1. These boron-containing compounds have found extensive applications in organic synthesis2, material science3, medicinal chemistry4, analytic chemosensing5, and chemical biology6. Notably, they are key coupling partners in Suzuki coupling reactions for carbon-carbon bond formation in organic synthesis and drug discovery2. As Lewis acid, boronic acids facilitate transitions between planar tricoordination and tetrahedral tetracoordination boron-center via reversible covalent bonding features7, holding many advances in self-assembled organic materials, chemoprobes and pharmacodynamic activities3,5,6 Moreover, the functional group of boronic acid can serve as ideal bioisostere for carboxylic acids, enhancing physiochemical properties in medicinal chemistry4. Consequently, facile installation of boronic acids from readily available chemicals is of significant synthetic importance, allowing for the widespread use of boronic acids in many fields of science (Fig. 1a). While radical borylation has advanced the production of aromatic boronic acids8,9,10, the catalytic radical borylation of C(sp3)-rich materials is still in its infancy11,12,13.

Fig. 1: Challenges and strategies in radical borylation of unactivated C-Cl bonds.
figure 1

a Current status of construction and applications of boron-containing compounds. b Chemical features and challenges of alkyl halides. c The state-of-the-art for photoinduced defunctionalization radical borylation. d Photoinduced gold-catalyzed divergent dechloroborylation of gem-dichloroalkanes.

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Alkyl halides, commonly used in organic chemistry, are ideal radical precursors for the preparation of alkyl boronic acids. Alkyl chlorides, more abundant and economical than alkyl iodides and bromides, have been less utilized due to their higher bond dissociation energy (BDE) (~84 kcal mol−1) and lower reduction potential (Ered = ~−2.8 V versus SCE)(Fig. 1b)14. Traditional stoichiometric methods, involving reactive organometallic reagents (alkyl-Li or alkyl-MgX), have limited the functional group tolerance15. Given the extensive use of alkyl boronic acids, there is a growing need for synthetic methodologies that can accommodate structural diversity and functional group tolerance. Transition metal-catalyzed radical borylation has become an emerging protocol but generally requirement of strong organic base16,17,18,19,20,21,22. For example, the Marder’s group disclosed several examples on Cu(II)-catalyzed gem-diborylation of dichloroalkanes in the presence of stoichiometric MeOK17. Recent advances in B-B bond activation include the Lu group’s electrochemical gem-diborylation of highly active gem-bromoalkanes via paired electrolysis23, as well as photoinduced defunctionalization radical borylation, which offers milder conditions and better versatility24. As illustrated in Fig. 1c, although C(sp3)-X (X = Br, I or other leaving groups) have been widely explored in visible-light-induced defunctionalization radical borylation11,25,26,27,28,29, few photocatalytic strategies are capable of homolytic conversion of C(sp3)-Cl bonds for radical borylation30,31. Inspired by the seminal works on gold-catalyzed C-X (X= Br, I) bond activation32,33,34,35,36,37,38,39, we have demonstrated that using dinuclear gold complexes and ligand micro-environmental change strategy can circumvent the high reduction potential of alkyl chlorides through inner-sphere electron transfer mechanism40. As a result, the unreactive gem-dichloroalknes, which are usually prone to proceed hydrogen atom transfer (HAT) reactions41, construct carbon-carbon bonds with various alkenes. In this context, we surmised the possibility of a divergent radical dechloroborylation protocol of readily available gem-dichloroalkanes, which will further expedite the next generation of borylation in the future (Fig. 1d). Its success can provide a direct and practical route to convert C(sp3)-Cl into a wide range of structurally diverse alkyl boronic, α-chloroboronic and gem-diboronic esters, and the scope is far beyond with previous defunctionalization radical borylation.

In this study, we herein disclose a dechlorinative radical borylation of gem-dichloroalkanes through photoexcited dinuclear gold catalysis. This method effectively utilizes a wide range of gem-dichloroalkanes, including dichloromethane, as starting materials. They can smoothly proceed gem-diborylation, monoborylation, and hydroborylation to produce structurally diverse high-value alkyl gem-diboronic, α-chloroboronic and boronic esters in moderate to good yields under mild conditions. Interestingly, employing a continuous-flow technique further enhances the efficiency of the dechloroborylation reaction. This demonstrates its unique reactivity and excellent functional group compatibility, thus facilitating the late-stage borylation of complex molecules.

Results

Reaction development

The reaction development was initiated by using commercially available (3,3-dichloropropyl)benzene (1a) and 2,2’-bis-1,3,2-benzodioxaborole (B2cat2) (2) as the model substrate. After investigation of various photocatalysts, boron sources, and solvents, the optimal conditions include the use of dinuclear gold-complex (PC1) as photocatalyst and B2cat2 as the radical boron-source with N,N-diethylformamide (DEF) as the solvent at room temperature, which can deliver the desired product (3) in 73% isolated yield (Table 1, entry 1). Notably, this kind of gem-diboronic esters42,43,44,45,46,47 are versatile building blocks in organic synthesis. When trinuclear gold-complex (PC2)48 was employed, only a trace amount of desired products were detected (Table 1, entry 2). [Au(dppm)Cl]2 (PC3)49,50,51 was employed under the same conditions, and the yield significantly decreased to 45% (Table 1, entry 3). Other commonly used photocatalysts, such as fac-Ir(ppy)3, Ru(bpy)3Cl2 and Eosin Y, all failed to achieve this transformation (Table 1, entries 4-6), possibly owing to their mechanistic limits to outer-sphere electron transfer52. Switching B2cat2 to B2pin2 led to no reaction (Table 1, entry 7). We speculated that the important role of the electron-rich aromatic diol ligand, catechol, on the boron reagent favors the radical borylation. Interestingly, it is found that DMF and NMP can also trigger radical borylation while MeCN gave rise to little products (Table 1, entries 8-10). We envisioned that the oxygen atom in DEF might coordinate with B2cat211, enabling the oxidation peak of B2cat2 shifted to more negative values, which can be rationalized by UV-Vis spectroscopy analysis, 11B NMR detection, and cyclic voltammetry (CV) experiments (see Supplementary Fig. 34, 46, and 56). In addition, it is found that the good solubility of DEF can give better results. The replacement of blue LEDs (λmax = 466 nm) with purple LEDs (λmax = 390 nm), a decreased yield was obtained (Table 1, entry 11). Control experiments showed that the absence of either the photocatalyst or light resulted in no products, indicating the necessity of these components in this dechlorinative gem-diborylation reaction (Table 1, entries 12 and 13).

Table 1 Optimization of the reaction conditionsa
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Substrate scope

With the optimal conditions in hand, we next investigated the substrate scope and generality of this dechlorinative diborylation protocol (Fig. 2). A series of (3,3-dichloropropyl)benzene derivatives could deliver the corresponding gem-diborylalkanes (3-13) in moderate to excellent yields. Interestingly, aryl rings bearing with fluoro- or chloro-substituents (8, 9) were tolerated well, facilitating downstream modification at the halogenated position. In addition, aryl rings bearing electron-withdrawing or electron-donating groups at either ortho-, meta- or para-positions delivered the desired products (6, 12, 13) in 56-85% yields. Importantly, the protocol exhibited excellent compatibility with useful functional groups, including nitriles, esters, and furan (10, 11, 14). Notably, substituted gem-dichloroalkanes are tolerated in this transformation and furnished the corresponding borylation products (15-17 and 20) in moderate yields. A range of densely functionalized gem-dichloroalkanes containing unsaturated bonds, such as internal alkyne, terminal, or internal alkenes, can uniformly proceed gold-catalyzed diborylation to give rise to products (18-21) in 63-71% yields.

Fig. 2: Substrate scope of gem-diborylation reaction.
figure 2

Reaction conditions: PC1 (3 mol%), gem-dichloroalkanes 1 (0.2 mmol), B2cat2 2 (4 equiv.), DEF (2 mL), blue LEDs, ambient temperature, 24 h; then pinacol (4 equiv.), Et3N (0.5 mL), 1 h. a5 equiv. B2cat2 were used.

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Intriguingly, the steric hindrance effect hardly influences this dechlorinative gem-borylation efficiency. For example, when the methyl group was introduced at the β-position of gem-dichloroalkanes, the desired products (22-26) were obtained in 48-75% yields. The other mono-substituted gem-dichloroalkanes can also proceed with this transformation smoothly to generate gem-diboronic esters (27 and 28) in moderate yields. Moreover, the highly sterically hindered double alkyl-substituted gem-dichloroalkanes, 4,4-dichlorotetrahydro-2H-pyran was subjected to the standard conditions, and it can deliver the expected product (29) in 70% yields. To demonstrate the practicability of this transformation, commercially available dichloromethane and deuterium-labelled dichloromethane also could be used to produce corresponding diboronic esters (30 and 31), which further illustrates that this strategy has promising advantages in organic synthesis.

Late-stage borylation of complex molecules represents the state-of-the-art in this field since the installation is generally at the early stage of synthesis owing to the technical difficulties in their preparation, thus severely compromising its total synthetic economy. In this protocol, gold-catalyzed dechlorinative gem-diborylation holds excellent functional group compatibility. A series of natural products and pharmaceuticals derivatives, including mitotan, oxaprozin, D-alphla-tocopherol succinate, linoleic acid, and chlorambucil were all suitable coupling partners and tolerated the conditions well, furnishing the corresponding products (32–36) in moderate yields.

With the success of gold-catalyzed dechlorinative gem-diborylation, we wonder whether the monoboronation of gem-dichloroalkanes could be achieved. If successful, it will provide a platform for the synthesis of substituted α-chloro alkylboronic esters, which are versatile building blocks in organic synthesis due to their amphiphilicity53. We found that gold-catalyzed dechlorinative monoborylation of very sterically hindered gem-dichloroalkanes can proceed smoothly, delivering the desired α-chloro alkylboronic esters in moderate to excellent yields (Fig. 3). A series of substituted cyclopropanes can successfully generate the corresponding monoborylation products (37 and 38). Gem-dichloroalkanes bearing fused rings were employed to react with B2cat2 (2) to afford the desired products (39–41) in 41–73% yields. The Bpin ester can be conveniently hydrolyzed to the corresponding boronic acid (39a). Furthermore, two alkyl groups were introduced at the β-position of gem-dichloroalkanes and furnished the monoborylation products (42 and 43) in moderate yields. In addition to pinacol esters, other borates can be conveniently obtained by trans-esterifying catechol ester intermediates. Thus, various five- and six-membered ring boronic acid derivatives were prepared in 60 to 80% yields (44–47), including (+)-pinacol diol (47) that is frequently encountered in stereoselective synthesis54.

Fig. 3: Substrate Scope of monoborylation reaction.
figure 3

Reaction conditions: PC1 (3 mol%), gem-dichloroalkanes 1 (0.2 mmol), B2cat2 2 (4 equiv.), DEF (2 mL), blue LEDs, ambient temperature, 24 h; then pinacol (4 equiv.), Et3N (0.5 mL),1 h. a39 (0.2 mmol), DEA (1.1 equiv.), ether, rt, ∼30 min followed by 0.1 M HCl (30 min).

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To our delight, when a certain amount of KF was added, α-hydroborylation of gem-dichloroalkanes can readily occur (see Supplementary Table 2 for details). The use of DMF-npentanol to replace DEF will further increase the reaction yields and thus was determined as the best solvent for selective hydroborylation of gem-dichloroalkanes. Under the modified reaction conditions, dechlorinative hydroborylation protocol can give rise to the desired products (48–66) in moderate to good yields. As shown in Fig. 4, phenylpropyl derivatives with both electron-withdrawing and electron-donating substituents at the para-position of the phenyl ring were all suitable under standard conditions. For example, a range of versatile functional groups, such as tert-butyl, phenyl, fluoro, and chloro on the aromatic ring uniformly gave the desired hydroborylation products (49–52) in 47–72% yields. Notably, both terminal alkene (57) and internal alkyne (58) can survive. Meanwhile, α-methyl substituted gem-dichloroalkanes also could be used for this gold-catalyzed protocol successfully, affording the corresponding products (59–61) in moderate yields. Different cyclic gem-dichloroalkanes, including cyclopropane, cyclopentane, and cyclohexane, can be converted into the target products (62–64). Complex gem-dichloroalkanes, such as the derivatives of mitotan (65) and oxaprozin (66), were found to be compatible, which demonstrates its generality and good functional group tolerance.

Fig. 4: Substrate scope of hydroborylation reaction.
figure 4

Reaction conditions: PC1 (3 mol%), gem-dichloroalkanes 1 (0.2 mmol), B2cat2 2 (3 equiv.), KF (3.5 equiv.), DMF/nPentanol (1:1, 2 mL), blue LEDs, ambient temperature, 24 h; then pinacol (4 equiv.), Et3N (0.5 mL),1 h. a4 equiv. of 2-tert-butyl-1,1,3,3-tetramethyl-guanidine (BTMG) were used.

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Synthetic application

To demonstrate synthetic utility, 10 mmol scale experiments with only 0.5 mol% catalyst loading of PC1 were performed (Fig. 5a). The corresponding target products (3, 39, and 48) were isolated in 61% (2.27 g), 65% (1.66 g) and 48% (1.18 g), respectively. In recent years, continuous-flow microtube reactors have provided a good platform for photochemical reactions due to the improved mass and heat transfer process55,56. Consequently, we tried to introduce this continuous-flow synthesis technology into the gold-catalyzed divergent dechlorinative borylation of gem-dichloroalkanes. As shown in Fig. 5b, diborylation, monoborylation, and hydroborylation of gem-dichloroalkanes were successfully achieved at 1 mmol scale within a shorter reaction time. Several functionalized products (3, 11, 17, 26, 31, 37, 50, and 57) were rendered in moderate to good yields. The continuous-flow technique could easily achieve 10 mmol scale production, delivering the target product (30) with 65% yield, which is the key building block for the synthesis of valuable drugs and natural products57.

Fig. 5: Synthetic applications.
figure 5

a Gram-scale experimental results. b Continuous-flow synthesis applications in dechlorinative borylation at the 1 mmol scale. aThe reaction was performed on a 10 mmol scale with 0.5 mol% catalyst loading TR, residence time; V, volume. c Diversification of products: (i) 3, allyl chlorides, NaOtBu, THF, rt, 3 h. (ii) Pd(PtBu3)2 (5 mol%), 3, 4-iodoanisole, KOH, H2O/1,4-dioxane, rt, 2 h. (iii) Pd(PtBu3)2 (5 mol%), 3, methyl 4-iodobenzoate, KOH, H2O/1,4-dioxane, rt, 2 h. (iv) 30, Quinoline, ZnMe2, LiOtBu, toluene, 120 oC, 3 h. (v) 30, 4-iodoanisole, NaOtBu, toluene/THF, 120 oC, 6 h. (vi) 39, allyl-MgBr, THF, −78 oC-rt, overnight.

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Importantly, these boron-containing products are versatile in terms of further synthetic transformation (Fig. 5c). For example, the borylation product (3) was treated with allyl chlorides in the presence of NatOBu, the SN2 substitution can readily occur to form a highly functionalized alkylboronic ester (67) in 63% yield. In addition, the gem-bis(boryl)alkane (3) can undergo Pd-catalyzed Suzuki-Miyaura coupling with 4-iodoanisole or methyl 4-iodobenzoate to give the coupling products (68 and 69) in 86% and 62% yields, respectively. Interestingly, 1,1-diborylmethanes (30) can be used as an alkylating reagent for the quinoline to afford C2-methylated product (70) in moderate yield. The reaction of 4-iodoanisole with 30 in the presence of NatOBu at 120 °C proceeded to furnish 4-methoxyphenyl boronate ester (71) in 75% yield. Also, treatment α-chloroboronate ester (39) with allyl magnesium bromides afforded the tertiary alkylboronate esters (72) in 70% yield. It is an important building block for the formation of sterically hindered quaternary carbon via 1,2-metallate rearrangements58.

Mechanistic studies

To gain insight into the mechanism of this gold-catalyzed dechlorinative borylation process, the model reaction was performed in the presence of radical scavenger (2,2,6,6-tetramethyl-1-piperidin-1-yl)oxyl (TEMPO), no desired product (3) was observed and the TEMPO-trapped chloroalkyl radical adduct was successfully detected by high-resolution mass spectrometry (HRMS; Fig. 6a). To investigate the possible intermediate of dechlorinative gem-diborylation, we performed the following control experiments (Fig. 6b). When the α-chloroboronic esters (74) were subjected to the standard conditions of diborylation, the expected gem-diborylated product (3) can be obtained in 70% isolated yield while no expected product was detected in the absence of dinuclear gold-catalyst (Fig. 6b-i). This would suggest that PC1 is essential for the generation of α-boryl radical intermediate. Under the standard reaction conditions of hydroborylation (Fig. 6b-ii), the α-chloroboronic esters (74) can deliver the hydroborylated product (48) in 58% isolated yield, which indicates that PC1, B2cat2, and KF were essential for this hydroborylation process. However, gem-diboronic esters (3) cannot give rise to hydroborylation product 48 under different conditions (Fig. 6b-iii), which further demonstrated that α-chloroboronic esters would be one possible intermediate for the hydroborylation product.

Fig. 6: Mechanism studies.
figure 6

a Radical inhibition experiments of the model reaction. b Control experiments. c UV-Vis absorption spectra in DEF and DCM, respectively. d 31P NMR monitoring experiments. e 11B NMR monitoring experiments.

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Subsequently, we performed the deuterium labelling experiments to determine the hydrogen source of this hydroborylation (Fig. 6b-iv). Under the modified standard conditions of hydroborylation with DMF/H2O instead of DMF/npentanol, (3,3-dichloropropyl)benzene (1a) can also furnish product (48) in 63% yields. Surprisingly, in the presence of either DMF/D2O or DMF(d-7)/H2O, moderate yield of expected products can be detected but with little deuterium incorporation. We envisioned that once water is involved in the reaction system, the rapid H/D exchange would enable H-atom transfer prior to the D-atom transfer. It is important to find that the deuterated product (48-D) was isolated in 54% yield with > 95% deuterium incorporation when DMF(d-7) was employed in the hydroborylation reaction (see Supplementary Fig. 25 for details). Moreover, the DFT calculation result indicates that the free energy barrier for H-atom transfer from water is as high as 56.9 kcal mol-1 (see Supplementary Fig. 62). These results together suggest that the hydrogen source of hydroborylation may originate from DMF.

In addition, we measured the UV-Vis spectra of the gold catalyst and corresponding substrates in different solvents of DEF and DCM (Fig. 6c). It was found that the gold catalyst (PC1) has a very weak absorption in the range of 400-500 nm. However, by mixing the gold catalyst (PC1) with B2cat2 (2) in DEF for the UV–Vis measurement, a shift was observed (Fig. 6c, left). By comparison of the UV-Vis spectra in DEF and DCM, the DEF would coordinate with B2cat2 to form a new complex of DEF-ligated B2cat211 (Fig. 6c, right). Consequently, we speculate that a suitably bound PC1/DEF-ligated B2cat2 complex might be formed to enhance its absorption under irradiation by blue LEDs.

To further demonstrate the interaction between PC1, B2cat2, and DEF, 31P NMR experiments were performed by using Ph3P as the external standard (Fig. 6d). When B2cat2 was added into the dinuclear gold-catalyst (PC1) solution in CD3CN, it is found that the chemical shift can shift from 51.85 ppm to 53.35 ppm while the addition of DEF would further result in another shift from 53.35 ppm to 53.13 ppm. It would further support the formation of a bound complex between PC1 and DEF-ligated B2cat2, consistent with previous UV-Vis spectra results. In addition, the 11B NMR spectra of B2cat2 with different equivalents of DEF can also confirm this. As shown in Fig. 6e, the 11B NMR signal of B2cat2 (31.08 ppm) increasingly shifted along with the addition of DEF and a relatively broad upfield signal of 25.05 ppm and sharp upfield signal of 13.27 ppm were observed when largely excess DEF (20 equiv.) was added. These new boron signals can be assigned to the ligated diboron-complex (B1) and Bcat2 complex (B2)11. Furthermore, our DFT calculations coupled with IGMH analysis reveal that PC1 and DEF-ligated B2cat2 can form a bound complex, characterized by a B-Cl distance of 2.05 Å and intermolecular interaction energy of -37.7 kcal mol-1 (Fig. 7a).

Fig. 7: Proposed mechanism and computational studies.
figure 7

a Reaction mechanism for gold catalyzed divergent dechlorinative borylation. SET single-electron transfer, HAT hydrogen atom transfer. b DFT calculation results of HAT process at the PBE (D3BJ)/def2-SVP/def2-TZVP/PCM(DMF)//RI-wB97M-V/def2-TZVPP/SMD(DMF) level of theory.

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Based on the above mechanistic experiments, a proposed mechanism for gold-catalyzed divergent dechloborylation is illustrated in Fig. 7a. First, the complexation of DEF and B2cat2 can generate DEF-ligated B2cat2 complex (75) in-situ. Its combination with photocatalyst (PC1) can generate a bound gold complex (76), which is supported by DFT, UV-Vis, and NMR. This species (76) then absorbs visible light to generate a triplet excited-state species (77). Significantly, a single-electron transition of the excited species will not only enhance the aurophilic interaction but also provide an increasing coordination number at the AuI site59. The existence of a lone-pair electron on the halogen atom facilitates the dynamic coordination between gem-dichloroalkanes and the excited-state complex (77) to form an exciplex (78), which undergoes an inner-sphere single electron transfer (SET) process to deliver the corresponding Au(I)-Au(II) intermediate as well as chloroalkyl radical species. Owing to the stronger electrostatic interaction of chloride towards Au(I)-Au(II) than Au(I)-Au(I), the bound complex between PC1 and DEF-ligated B2cat2 will become much weaker. Consequently, the produced chloroalkyl radical can proceed with the rapid radical attack to DEF-ligated B2cat2 to generate the α-chloroboronate species (80) and release Au(I)-Au(II) species (81) as well as the carbon-centered α-aminoalkyl radical (82). Subsequently, this species (82) is able to proceed with single electron oxidation by Au(I)-Au(II) to generate the Bcat-DEF adducts (83), thus completing the gold-catalyzed photoredox cycle. On the other hand, the resulting α-chloroboronate species (80) can similarly undergo the relay functionalization to give rise to the gem-diborylated products (84) via the second radical borylation, while hydroborylated products (85) via hydrogen atom transfer (HAT) with solvents. As fluoride is an important factor for a high yield in the hydroborylation, we envisioned that it would be a good mediator to interact with the boron center and DMF to generate complex 8660, facilitating the HAT process. To figure out the influence of fluoride anions on the HAT process, further theoretical calculations were performed (Fig. 7b). It is interesting to find that the free energy barrier of the transition state in the HAT process is 13.4 kcal mol-1, which is much lower than that of direct HAT with DMF (TS-2: 17.9 kcal mol-1) (see computational details in Supplementary Discussion). The computed energy profile shows the superiority of the HAT process assistance with the fluoride over the direct HAT process.

Discussion

In summary, we have developed a divergent radical dechloborylation of readily available gem-dichloroalkanes, facilitated by dinucelar gold catalysis and visible light irradiation. A wide range of structurally diverse high-value alkyl boronic, α-chloroboronic, and gem-diboronic esters can be constructed from parent gem-dichloroalkanes in moderate to good yields (>60 examples, up to 92% yields) under mild conditions. Notable for its excellent functional group tolerance, this protocol is particularly effective for late-stage radical borylation of complex molecules and the derivatives of biologically important molecules. Thus, gem-diborylation, monoborylation, and hydroborylation can diversify the alkyl boronic acids, complementing the known defunctionalization radical borylations. Moreover, the utilization of continuous-flow synthesis can further improve the decholoborylation efficiency, allowing for gram-scale preparation.

Methods

General procedure for geminal diborylation of gem-dichloroalkanes

To an oven-dried 10 mL sealed tube, PC1 (3 mol%, 0.006 mmol, 7.7 mg), gem-dichloroalkanes 1 (0.2 mmol), B2cat2 2 (0.8 mmol, 190 mg, 4 equiv.) and DEF (2 mL) are successively added and the tube is backfilled with argon three times under Schlenk line. The resulting reaction mixture is vigorously stirred under the irradiation of blue LEDs (distance app. 4 cm from the bulb) at ambient temperature (the fan was used to keep the reaction temperature around ambient temperature) for 24 h. Subsequently, a solution of pinacol (0.8 mmol, 4 equiv., 94.4 mg) in triethylamine (0.5 mL) is added to the resulting crude and the reaction mixture is kept stirring at room temperature for another 1 h. Then, saturated brine water (10 mL) is added to the reaction mixture and the aqueous layer is extracted with ethyl acetate (3 × 5 mL). The organic layers are combined, dried over Na2SO4, filtered, and concentrated. The crude residue is directly purified quickly by silica column chromatography (eluted with ethyl acetate/petroleum ether) to yield the desired gem-diborylation products.

General procedure for monoborylation of gem-dichloroalkanes

To an oven-dried 10 mL sealed tube, PC1 (3 mol%, 0.006 mmol, 7.7 mg), gem-dichloroalkanes 1 (0.2 mmol), B2cat2 2 (0.8 mmol, 190 mg, 4 equiv.) and DEF (2 mL) are successively added and the tube is backfilled with argon three times under Schlenk line. The resulting reaction mixture is vigorously stirred under the irradiation of blue LEDs (distance app. 4 cm from the bulb) at ambient temperature (the fan is used to keep the reaction temperature around ambient temperature) for 24 h. Subsequently, a solution of pinacol (0.8 mmol, 4 equiv., 94.4 mg) in triethylamine (0.5 mL) is added to the resulting crude and the reaction mixture is kept stirring at room temperature for another 1 h. Then, saturated brine water (10 mL) is added to the reaction mixture and the aqueous layer is extracted with ethyl acetate (3 × 5 mL) three times. The organic layers are combined, dried over Na2SO4, filtered, and concentrated. The crude residue is directly purified quickly by silica column chromatography (eluted with ethyl acetate/petroleum ether) to yield the desired monoborylation products.

General procedure for hydroborylation of gem-dichloroalkanes

To an oven-dried 10 mL sealed tube, PC1 (3 mol%, 0.006 mmol, 7.7 mg), gem-dichloroalkanes 1 (0.2 mmol), B2cat2 2 (0.6 mmol, 142 mg, 3 equiv.), KF (0.7 mmol, 41 mg, 3.5 equiv.) and DMF/nPentanol (1:1, 2 mL) are successively added and the tube is backfilled with argon three times under Schlenk line. The resulting reaction mixture is vigorously stirred under the irradiation of blue LEDs (distance app. 4 cm from the bulb) at ambient temperature (the fan is used to keep the reaction temperature around ambient temperature) for 24 h. Subsequently, a solution of pinacol (0.8 mmol, 4 equiv., 94.4 mg) in triethylamine (0.5 mL) is added to the resulting crude and the reaction mixture is kept stirring at room temperature for another 1 h. Then, saturated brine water (10 mL) is added to the reaction mixture, and the aqueous layer is extracted with ethyl acetate (3 × 5 mL) three times. The organic layers are combined, dried over Na2SO4, filtered, and concentrated. The crude residue is directly purified quickly by silica column chromatography (eluted with ethyl acetate/petroleum ether) to yield the desired hydroborylation products.