Asymmetric aldol additions using chlorotitanium enolates of N-acyl oxazolidinones, oxazolidinethiones and thiazolidinethiones proceed with high diastereoselectivity for the ‘Evans syn’ product using one equivalent of titanium tetrachloride, one equivalent of diisopropylethylamine and one equivalent of N-methyl-2-pyrrolidinone. Typical selectivities of 94:6 to >98:2 were obtained using N-propionyl oxazolidinones, oxazolidinethiones and thiazolidinethiones at 0 °C with stoichiometric amounts of aldehyde. Glycolate imides also gave high selectivities and high yields using this procedure.
不对称的醛醇加成反应,使用N-酰基
噁唑烷啉酮、
噁唑烷
硫酮和
噻唑烷
硫酮的
氯钛烯醇盐,在反应中加入1当量的
四氯化钛、1当量的
二异丙基乙胺和1当量的N-甲基-
2-吡咯烷酮,能够以高的非对映选择性得到“Evans syn”产物。使用N-丙酰基
噁唑烷啉酮、
噁唑烷
硫酮和
噻唑烷
硫酮在0 °C下与
化学计量量的醛反应,通常获得的选择性为94:6到>98:2。使用该方法,
乙二醇酰亚胺同样获得了高选择性和高产率。