Regioselective ring opening of exo- and endo-3,4-benzylidene acetals of arabinopyranoside derivatives with Lewis acids and reducing agents
作者:Janjira Rujirawanich、Boonsong Kongkathip、Ngampong Kongkathip
DOI:10.1016/j.carres.2011.01.031
日期:2011.5
Dioxolane type 3,4-benzylidene acetals of benzyl beta-l-arabinose either as a mixture or pure exo- and endo-isomers cleavaged with BF(3).OEt(2)/Et(3)SiH in dichloromethane or acetonitrile regioselectively, provided the 4-O-benzyl-3-hydroxy derivative. The reaction with TiCl(4)/Et(3)SiH or Cu(OTf)(2)/Et(3)SiH provided a mixture of 3- and 4-O-benzyl derivatives whereas with Cu(OTf)(2)/BH(3).THF gave
苄基β-1-阿拉伯糖的二氧戊环3,4-亚苄基乙缩醛的混合物或纯的外向和内向异构体,用BF(3).OEt(2)/ Et(3)SiH在二氯甲烷或乙腈中区域选择性地裂解,提供了4-O-苄基-3-羟基衍生物。与TiCl(4)/ Et(3)SiH或Cu(OTf)(2)/ Et(3)SiH的反应提供了3-和4-O-苄基衍生物的混合物,而与Cu(OTf)(2)/ BH(3).THF仅得到水解产物。证明该反应的区域选择性由C-2处的乙酰基取代指导。苄基取代提供了3:1和4-O-苄基衍生物的混合物,而未取代则产生了2:1比率的相同混合物。