A general photo-induced wide-scope regioselective hydroboration of alkenes without using a photocatalyst or an external initiator

Abstract

Despite the recent development of boryl radical reactions, current methods to generate them relying on the photocatalysts or radical initiators cause contamination of the reaction. Herein, a novel system for...

Visible-light-induced 1,2-diphenyldisulfane-catalyzed regioselective hydroboration of electron-deficient alkenes

“…Importantly, the regioselectivity of this protocol is remarkable. According to the literature [30][31][32] and our previous results, 46 we systematically summarized the regioselectivity of this reaction in our recent work. 46 When b-aryl substituted a,b-unsaturated carbonyl substrates were used, the stabilized effect of the b-aryl group on the formed radical through the conjugated effect plays a major role to obtain the a-selectivity of the product.…”

“…According to the literature [30][31][32] and our previous results, 46 we systematically summarized the regioselectivity of this reaction in our recent work. 46 When b-aryl substituted a,b-unsaturated carbonyl substrates were used, the stabilized effect of the b-aryl group on the formed radical through the conjugated effect plays a major role to obtain the a-selectivity of the product. When b-alkyl substituted a,b-unsaturated carbonyl substrates were employed, the nucleophilicity of the boryl radical and the stabilization of the carbonyl group synergistically helps to achieve the b-regioselectivity.…”

Lewis Base–Boryl Radicals Enabled Borylation Reactions and Selective Activation of Carbon–Heteroatom Bonds

“…Zhu and Li disclosed the photocatalyzed reaction of NHC–BH 3 and Morita–Baylis–Hillman adducts, affording functionalized allyl boron compounds . Very recently, Chen and Liu described a novel approach for generation of NHC–boryl radicals with thiol catalyst, in which boryl radicals were produced by B–S bond homolytic cleavage of in situ formed boryl sulfides under light irradiation . Ye also developed a photoredox protocol for single electron oxidation of an amine–borane complex to generate the corresponding boryl radical …”

“…31 These boryl radicals have shown different reactivities in comparison with carbon radicals, while they exhibit some similarities with stannyl radicals, such as the addition to xanthates, halogen atom abstraction, and polymerization of electron-deficient alkenes. Despite these significant findings, there still remains a large room to exploit more interesting synthetic applications, because (i) LBRs were mainly used as mediators but rarely served as valuable borylation reagents for C−B bond formation, 30,32 (ii) the generation pathway of LBRs largely relied on HAA from the corresponding Lewis base−borane with the aid of a radical initiator at elevated temperature whereas new approaches (i.e., single electron transfer) under milder reaction conditions remain less known, 33,34 With these considerations, we began our studies in exploring new transformations of LBRs in 2015. We envisioned that adjusting the Lewis base motif and the boron substituents could modulate the structure and reactivity of LBRs, 35 thus offering more opportunities to discover new reaction mechanisms and strategies for selectivity control.…”

Transition metal-free radicaltrans-hydroboration of alkynes with NHC-boranesviavisible-light photoredox catalysis

“…11 Most recently, photoredox hydroboration of electron-deficient alkenes has also been developed using Ir photocatalysts 9 b ,12 or organic photocatalysts. 13 Despite this progress, the majority of reported methods are limited to specific alkenes. The further exploitation of photoredox radical borylation with NHC-boranes is still of great importance to enrich the organoboron library.…”