Reversal of stereoselectivity in the Evans aldol reaction of α,α-difluoro and α,α,α-trifluoro carbonyl compounds
作者:Katsuhiko Iseki、Satoshi Oishi、Yoshiro Kobayashi
DOI:10.1016/0040-4020(95)00858-6
日期:1996.1
The Evans aldol reaction of hexafluoroacetone and trifluoroacetaldehyde causes complete reversal of diastereofacial selectivity. The boron enolate derived from N-acyloxazolidinone 2 reacts with trifluoroacetaldehyde to give anti and “non-Evans” syn aldols with stereoselectivity in the range of 7:3–17:3. With α,α-difluoroaldehyde 4b, a small amount of the normal syn aldol was formed. However, the anti
六氟丙酮和三氟乙醛的埃文斯醛醇醛缩合反应完全逆转了非对映选择性。衍生自N-酰基氧杂唑烷酮2的烯醇硼与三氟乙醛反应生成立体选择性为7:3-17:3的抗和“非Evans”顺式醇醛。与α,α-二氟醛4b一起,形成少量的正常顺式醇醛。但是,抗羟醛是主要产品。