Catalytic Enantioselective Allylboration of Ketones

Abstract

The first example of catalytic enantioselective allylboration and crotylboration of simple ketones is described. High enantioselectivity (up to 93% ee) was obtained using 3 mol % CuF-iPr-DuPHOS as a chiral catalyst and 4.5 mol % La(OiPr)3 as a cocatalyst. Mechanistic studies strongly suggested that the active nucleophile of the present reaction is an allylcopper, and that La(OiPr)3 facilitates the generation of an active allylcopper from the allylboronate, without affecting the transition-state structure of the ketone allylation step.

Lewis Base Catalysis in Organic Synthesis

“…[222, 227a-b, 314] An alternative strategy for developing an asymmetric, fluoride-catalyzed reaction of silylated pronucleophiles would be to combine the achiral, n-s* catalysis provided by fluoride ions with traditional chiral Lewis acid catalysis. This strategy has been reduced to practice in aldol reactions, [380] allylations, [381] cyanomethylations, [382] vinylations, and phenylations [383] with silylated pronucleophiles. The most thoroughly investigated examples in this class of reactions are silver(I) fluoride and copper(I) fluoride catalyzed aldol reactions.…”

Multimetallic Multifunctional Catalysts for Asymmetric Reactions

“…Because Bu 4 NCl itself promoted racemic proton migration to some extent, the amount of Bu 4 NCl must be much smaller (Â1/5) than the amount of the asymmetric yttrium catalyst. After enantiomerically pure 21 was produced via recrystallization, an allyl group was introduced with excellent diastereoselectivity (14:1) under the modified conditions using CuF catalysis [57,58] developed in our group (Scheme 14, from 21 to 23). Addition of 15 mol% KO-tBu accelerated the reaction, and a combination of ZnCl 2 and Bu 4 PBF 4 markedly improved the diastereoselectivity.…”

Low‐Valent Indium as a Catalyst for the Allylation of Ketones and N‐Acylhydrazones

“…[2] A great number of allylation reactions have been developed using stannanes, [3] silanes, [4] and boron reagents. [5] Although a variety of protocols exist for the allylation of ketones, most are lacking in substrate generality and there exists a need to develop new catalytic allylation reactions that overcome this limitation.…”