Radical Hydroboration and Hydrosilylation of gem-Difluoroalkenes: Synthesis of α-Difluorinated Alkylborons and Alkylsilanes

Abstract

A first example of radical hydroboration and hydrosilylation of gem-difluoroalkenes using ABIN as the radical initiator is described. This protocol features good functional group tolerance, operational simplicity, high atom economy, and easy scale-up, enabling efficient assembly of a wide range of α-difluorinated alkylborons and alkylsilanes in moderate to excellent yields. The synthetic utility of these products is demonstrated by further transformation of the C− B bond and C−Si bond into valuable CF 2 -containing molecules.

Fluorine-Retentive Strategies for the Functionalization of gem-Difluoroalkenes

“…Specifically, Rh-catalyzed hydroboration (Scheme 37B) 84 or radical hydrosilation of gem-difluoroalkenes generated organometal intermediates, and subsequent protodeboronation or desilylation using TBAF delivers the product of net reductions (Scheme 37C). 70 Notably, the initial formation of the C-B and C-Si bonds occurs with distinct regioselectivities, and the respective boryl or silyl intermediates might be useful for other cross-coupling reactions. Of note, gem-difluoroalkenes are unreactive with NaBH4 and LiAlH4 as these reductants were used to reduce ketones and aldehydes in the precents of gem-difluoroalkenes.…”

Photoredox‐Controlled β‐Regioselective Radical Hydroboration of Activated Alkenes with NHC‐Boranes

“…[10b, 11a] Two paralleled pathways may account for a higher yield in the presence of thiol (27 % vs. 77 %). Subsequently, the radical addition of the NHC-boryl radical to the unsaturated carboncarbon double bond can afford radical intermediate (12), which further accepts one electron from Ir II to complete the photoredox cycle and generates intermediate (13), which can get one proton from (7 a) or t BuSH to afford the desired product 8 a. Indeed, the photoredox catalysis is a key factor to achieve b-regioselective radical hydroborylation of unsaturated amides compared to Wangs work.…”

“…During the process of this work, Wang and co-workers reported an elegant radical a-borylation of a,b-unsaturated carbonyl compounds with NHC-boranes using azodiisobutyronitrile (AIBN) as the radical initiators at 80 8C (Scheme 1 b). [12] However, in some case, a significant amount of regioisomeric products can be formed dependent on the electronic effect of substituents (a:b ranges from > 99:1 to 62:38).…”

Synthesis of Fluorinated Aminoalkylboronic Acids from Amphoteric α‐Boryl Aldehydes

“…[20] Until now, it has not been possible to prepare stable a-fluorinated free boronic acids. [20][21][22][23][24][25] The difficulty in making the free boronic acid forms of these molecules arises from the fact that the B-CF n motifs are unstable when boron is in tricoordinate form. [26][27][28] Though tolerant of oxygen atmosphere, molecules that feature the B-CF n functionality are prone to intramolecular rearrangements and can decompose upon heating or exposure to moisture (Figure 1 b).…”