Switchable Synthesis of Z‐Homoallylic Boronates and E‐Allylic Boronates by Enantioselective Copper‐Catalyzed 1,6‐Boration

Abstract

The enantioselective Cu-catalyzed 1,6-boration of (E,E)-α,β,γ,δ-unsaturated ketones is described, which gives homoallylic boronates with high enantiomeric purity and unexpectedly high Z-selectivity. By changing the solvent, the outcome can be altered to give E-allylic boronates.

Copper-Catalyzed Borylative Difunctionalization of π-Systems

“…The Meek group found that vinylboronates could serve as precursors to hydroxy bis(boronates) (Scheme 61). 158 The syn-diastereomer underwent elimination during silica gel chromatography, affording exclusively the anti-diastereomer (241). The products were obtained in good yields and enantioselectivities with a variety of aryl, alkyl, and alkenyl aldehydes, although the intermolecular variant was only explored with vinylboronate (239).…”

Ruthenium(ii)-catalyzed regioselective 1,6-conjugate addition of umpolung aldehydes as carbanion equivalents

“…47 The utility of the reaction was further examined on linear and cyclic aliphatic aldehydes with increased base loading, generating the desired products 34-35 in lower yields. For the conjugated electrophile, both electron-withdrawing and donating groups on the aryl ketone provided the desired 1,6addition products in moderate to good yields (36)(37)(38)(39)(40)(41)(42)(43). The thiophene-derived heteroarene ketone also led to a moderate yield (44).…”

“…31,32 Alternative transition-metal catalyzed 1,6-additions have been developed by Hayashi with rhodium, 11 cobalt, 33 and iridium catalysts. 34,35 Expansion of metal-catalyzed 1,6-additions to boryl and silyl groups are represented by the works of Lam, 36,37 Liao 38 and Newhouse. 39 While these advancements are very signicant, most involve stoichiometric use of organometallic nucleophiles, which inevitably leads to sizable metallic waste and poor atom economy.…”

Copper(I)‐Catalyzed Asymmetric Conjugate 1,6‐, 1,8‐, and 1,10‐Borylation

“…The similar reaction tendency was also observed in the copper(I)‐catalyzed enantioselective 1,6‐borylation of α,β,γ,δ‐unsaturated phosphonates [9b] . In 2018, the Lam group found that both Z ‐allylic and E ‐allylic boronates can be obtained as the major product with high enantioselectivity, simply by tuning the reaction solvent and the concentration in the copper(I)‐catalyzed 1,6‐borylation of α,β,γ,δ‐unsaturated ketones [9c] …”