An enantioselective allenylation of aldehydescatalyzed by a chiral, nonracemic phosphoricacid was reported. Under the developed conditions, 1,1′‐disubstituted allenic alcohols were obtained in 64–98% yields with 88–99% ee. Computational studies were conducted to probe the origin of asymmetric induction. Mechanistic studies suggest that the pinacol moiety of the propargylboronate is critical to the
substrates 1 and 2 can be regioselectively converted into chiral allenyl alcohols 3 through the title reaction [Eq. (1)] with the synergetic reagent iPrSBEt2 and a chiral TiIV catalyst. The dramatic regioselectivity originates from the regulation of the equilibriumbetween propargyl- and allenylstannanes during the catalytic process.
Chiral Silver Phosphate-Catalyzed Cycloisomeric Kinetic Resolution of α-Allenic Alcohols
作者:Yan Wang、Kuan Zheng、Ran Hong
DOI:10.1021/ja300453u
日期:2012.3.7
A kinetic resolution of a-allenic alcohols is realized through chiral silver phosphate-catalyzed cycloisomerization with high stereoselectivity (selectivity factor up to 189) and tolerance of a variety of functional groups. A mechanistic model is proposed to interpret the origin of the high stereoselectivity and broad substrate scope.