Highly Regio‐ and Enantioselective Copper‐Catalyzed Hydroboration of Styrenes

Abstract

An existing challenge is the development of efficient regioselective catalytic systems that are compatible with stable hydroboration reagents and can be rendered enantioselective by the use of nonracemic ligands. Copper(I) complexes with chelating phosphines catalyzed the regio‐ and enantioselective hydroboration of styrenes with pinacolborane (PinBH) at room temperature to afford the corresponding branched boronate esters (see example).

Copper-Catalyzed Recycling of Halogen Activating Groups via 1,3-Halogen Migration

“…For some of these cases, the benzyl bromide products were sensitive to elimination and were trapped with propargyl alcohol prior to isolation, illustrating the potential of this chemistry in cascade reactions to construct more complex compounds. Consistent with prior observations 5a , the 4-methoxy substrate (entry 12) reacted slowly. Finally, substitution on the β carbon of the styrene (entry 13) was tolerated in the 1,3-halogen migration, as trans- β-methylstyrene 4l gave 5l in 75% yield.…”

“…5 While none of the desired hydroboration was noted, due mainly to polymerization of the styrene, we observed small amounts of an unexpected by-product 2 . Curious as to whether 2 might be obtained exclusively, we undertook an investigation of several mono- and bidentate ligands for CuCl (Table 1).…”

[Cp*IrCl2]2 catalyzed hydroborations of alkenes using a bulky dioxaborocine

“…To gain further insight into the nature of products formed during these reactions, we therefore investigated reactions of vinylarenes using HBdd and [Cp*IrCl 2 ] 2 as a catalyst precursor. Considerable recent interest has focussed on the hydroboration [32][33][34][35][36][37][38] and subsequent transformation [39] of these important substrates. While reactions of 4-vinylanisole (4-MeOC 6 H 4 CH@CH 2 ) with HBcat and HBpin using a catalytic amount of [Cp*IrCl 2 ] 2 proceed to give the terminal hydScheme 1.…”

A mild copper catalyzed method for the selective deprotection of aryl allyl ethers

“…Similar copper boryl reagent combinations to those described in this report have been shown to promote a diverse array of transformations, including the hydroboration of alkenes and alkynes, [12][13][14][15][16] the borylation of aldehydes and imines, β-borylation of α,β-unsaturated carbonyl compounds 13,[17][18][19][20][21] and a variety of C-X borylations to generate aryl, alkyl and allyl boronates. 11,[22][23][24][25][26][27][28] Of these, the current reaction has closest parallels with the last of these transformations for which an S N 2' type displacement is commonly invoked.…”