Title: Rhodium-catalyzed Asymmetric 1,4- Addition of 3-Thiopheneboronic Acid to a,b-Unsaturated Carbonyl Compounds
Abstract:Abs tract -Asymmetric 1,4-addition of 3-thiopheneboronic acid to α,βunsaturated carbonyl compounds proceeded with high enantioselectivity in the presence of 3 mol% (Rh) of [Rh(OH)((S)-binap)] 2 in dio...Abs tract -Asymmetric 1,4-addition of 3-thiopheneboronic acid to α,βunsaturated carbonyl compounds proceeded with high enantioselectivity in the presence of 3 mol% (Rh) of [Rh(OH)((S)-binap)] 2 in dioxane/H 2 O (10/1) at 40 °C to give the corresponding optically active β-(3-thienyl) carbonyl compounds of over 94% ee.Asymmetric 1,4-addition of organometallic reagents to α,β-unsaturated carbonyl compounds is a useful process giving enantiomerically enriched β-substituted carbonyl compounds. 1As one of the most promising methods for the asymmetric 1,4-addition, the addition of aryl-and alkenylboronic acids under catalysis by chiral phosphine-rhodium complexes has been rapidly developed. 2-4However, to our best knowledge, heteroaromatic groups have not been introduced enantioselectively by the rhodium-catalyzed asymmetric 1,4-addition, 5 probably due to the instability of the corresponding boronic acids under the reaction conditions, the reactions typically being carried out with Rh(acac)((S)-binap) as a catalyst in dioxane/H 2 O at 100 °C. 2 During our recent studies on the catalytic cycle of the rhodium-catalyzed asymmetric 1,4-addition, 6 we found that [Rh(OH)((S)-binap)] 2 is much more catalytically active, which † Dedicated to Professor Yuichi Kanaoka on the occasion of his 75th birthday.Read More