The enolates of (+)- and (-)- menthyl acetate, formed by transmetallation from lithium with chloro ( cyclopentadienyl )bis(1,2:5,6-di-O-isopropylidene-α-D-glucofuranosato-O3)titanium [ CpTi (DAGO)2Cl] (1), react with benzaldehyde from the Re-face with high stereoselectivities (95 and 92% diastereomeric excess) when 12-crown-4 is used during the transmetallation . Use of the chiral cyclopentadienyltitanium-α,α,αα,αα-tetraaryl-2,2-dimethyl-1,3-dioxolan-4,5-dimethanol (TADDOL) complex (3) gives lower diastereoselectivities (58 and 40%) but the Si -face of benzaldehyde is attacked preferentially. Transmetallation of the 2-methylprop-2-enyl moiety to CpTi (DAGO)2Cl gives an allyltitanium reagent (2) which reacts with benzaldehyde from the Re-face with 88% enantiomeric excess.
锂与
氯(
环戊二烯基)双(1,2:5,6-di-O-isopropylidene-α-D-glucofuranosato-O3)tiTAnium [ CpTi (
DAGO)2Cl](1),当在反
金属化过程中使用 12-crown-4 时,可与 Re-face 中的
苯甲醛发生高立体选择性反应(非对映过量率分别为 95% 和 92%)。使用手性
环戊二烯基
钛-α,α,α,αα-四芳基-2,2-二甲基-
1,3-二氧戊环-4,5-二
甲醇 (TADDOL) 复合物 (3) 的非对映选择性较低(58% 和 40%),但
苯甲醛的 Si - 面优先受到攻击。将 2-甲基丙-2-烯基分子与 CpTi (
DAGO)2Cl 进行反
金属化反应,可得到烯丙基
钛试剂 (2),该试剂与
苯甲醛的反应对映体过量率为 88%。