Enantiopure building blocks for the synthesis of 3-methyl-2-alkanols. Diastereoselective methylmetal addition to a chiral 2-methylaldehyde followed by lipase catalysed esterification
作者:Michael Larsson、Jimmy Andersson、Rong Liu、Hans-Erik Högberg
DOI:10.1016/j.tetasy.2004.07.049
日期:2004.9
which left (2R,3R)-3-methyl-4-(phenylsulfanyl)butan-2-ol (2R,3R)-2 of 98:2 dr and 99% ee as the remaining substrate. The individual enantiomers of 2-methyl-3-(phenylsulfanyl)propanal 1 were prepared from readily available (S)- and (R)-3-hydroxy-2-methylpropanoic acid methyl ester and reacted with dimethylzinc to give both enantiomers of (2R*,3R*)-3-methyl-4-(phenylsulfanyl)butan-2-ol (2R, 3R)- or (2S
以高非对映异构体比[95:3]获得了外消旋合成结构单元(2 R *,3 R *)-3-甲基-4-(苯硫基)丁丹-2-醇(2 R *,3 R *)- 2。 5,(2 R *,3 R *)/(2 R *,3 S *)-比率是由路易斯酸催化的二甲基锌加成外消旋的2-甲基-3-(苯基硫烷基)丙醛(rac - 1)。由Chirazyme L-2(固定化南极假丝酵母脂肪酶B,CAL-B)催化的醋酸乙烯酯连续两次酰化反应导致四种立体异构体中的三种被优先酯化(2 S,3 S)98:2 dr和98%ee的)-3-甲基-4-(苯基硫烷基)丁-2-醇(2 S,3 S)-2。在第一个CAL-B催化的酰化步骤中获得的(2 R,3 R)-3-甲基-4-(苯基硫烷基)丁-2-醇(2 R,3 R)-2的立体异构不纯乙酸盐为使用CAL-A(固定的Novozyme SP 525)作为催化剂进行水解和再酯化,留下(2 R,3