Ir-Catalyzed Regioselective Dihydroboration of Thioalkynes toward Gem-Diboryl Thioethers

Abstract

While 1,1-diboryl (gem-diboryl) compounds are valuable synthetic building blocks, currently, related studies have mainly focused on those 1,1-diboryl alkanes without a hetero functional group in the α-position. gem-Diboryl compounds with an α-hetero substituent, though highly versatile, have been limitedly accessible and thus rarely utilized. Herein, we have developed the first α-dihydroboration of heteroalkynes leading to the efficient construction of gem-diboryl, hetero-, and tetrasubstituted carbon centers. This straightforward, practical, mild, and atom-economic reaction is an attractive complement to the conventional multistep synthetic strategy relying on deprotonation of gem-diborylmethane by a strong base. Specifically, [Ir(cod)(OMe)] 2 was found to be uniquely effective for this process of thioalkynes, leading to excellent α-regioselectivity when delivering the two boryl groups, which is remarkable in view of the many competitive paths including monohydroboration, 1,2-dihydroboration, dehydrodiboration, triboration, tetraboration, etc. Control experiments combined with DFT calculations suggested that this process involves two sequential hydroboration events. The second hydroboration requires a higher energy barrier due to severe steric repulsion in generating the highly congested α-sulfenyl gemdiboryl carbon center, a structural motif that was almost unknown before.

Diborodichloromethane as Versatile Reagent for Chemodivergent Synthesis of gem‐Diborylalkanes

“…α ‐Heteroatom (O, N, S) substituted gem ‐diboryl compounds have been rarely synthesized [10c,18] . With DBDCM, the consecutive C−Cl functionalizations with carbon nucleophile and heteroatomic nucleophile provide an access to diverse α ‐heteroatom substituted gem ‐diboryl compounds.…”

Organic Base-Facilitated Thiol–Thioalkyne Reaction with Exclusive Regio- and Stereoselectivity

“…23 was prepared as a colorless oil according to general procedure A in 93% yield (398.5 mg; elute: PE/ EA = 5:1, R f = 0.1): 1 (24). 24 was prepared as a pale yellow oil according to general procedure A in 72% yield (231.8 mg; elute: PE/EA = 1:2, R f = 0.2): 1 (26). 26 was prepared as a pale yellow oil according to general procedure A in 83% yield (167.9 mg; elute: PE/EA = 3:1, R f = 0.5): 1 H NMR (400 MHz, CDCl 3 ): δ 7.45−7.42 (m, 2H), 7.37− 7.31 (m, 4H), 7.29−7.24 (m, 1H), 6.94 (s, 1H), 6.80−6.76 (m, 2H), 5.50 (s, 1H), 4.17 (s, 2H), 0.89 (s, 9H), 0.04 (s, 6H); 13 (28).…”

“…Thioalkynes are one type of electron-rich internal alkynes exhibiting unique reactivities in a variety of transformations, such as hydrosilylation, − hydroboration, cycloaddition with different partners, − etc. One emblematic instance is the annulation of thioalkynes with organic azides under mild iridium catalysis, which displays regiospecificity in the generation of fully substituted 1,2,3-triazoles .…”

“…11−13 Introduction of electron-withdrawing groups (EWGs) could lead β addition in a nucleophilic manner; howbeit, achieving absolute stereoselectivity, which has been demonstrated to be critical in determining material behaviors, 14−16 is still an issue (Scheme 1B). 17−21 Thioalkynes are one type of electron-rich internal alkynes exhibiting unique reactivities in a variety of transformations, 22 such as hydrosilylation, 23−25 hydroboration, 26 cycloaddition with different partners, 27−35 etc. One emblematic instance is the annulation of thioalkynes with organic azides under mild iridium catalysis, which displays regiospecificity in the generation of fully substituted 1,2,3-triazoles.…”

Regio- and stereospecific thiol-thioalkyne reaction facilitated by organic base

“…[12][13][14] Introduction of electronwithdrawing groups (EWG) could lead  addition in a nucleophilic manner, howbeit achieving stereospecificity, which has demonstrated to be critical in determining material behaviours, [15][16][17] is still an issue (Scheme 1b). [18][19][20][21][22] Thioalkynes are one type of electron-rich internal alkynes exhibiting specific reactivity in a variety of transformations, 23 such as hydrosilylation, [24][25][26] hydroboration, 27 and cycloaddition with different partners, [28][29][30][31][32][33][34][35][36] etc. One emblematic instance is the annulation of thioalkynes with organic azides under mild iridium catalysis, which displays regiospecificity in the generation of fully substituted 1,2,3-triazoles.…”