Abstract Cycloaddition of 2-(β- d -ribofuranosyl)furan ( 1 ) with maleimide followed by treatment with acetone-TsOH gave a mixture of four diastereomers 3a–d , which were separated by preparative t.l.c. The absolute stereochemistry of each was determined. The endo ( 3a and 3b )/exo ( 3c and 3d ) ratio of cycloadducts was ∼11:1 and the ratio of 3a (1 R ,4 S ) and 3b (1 S ,4 R ) was ∼3:1. The Diels-Alder
摘要用马来
酰亚胺将2-(β-d-
呋喃核糖基)
呋喃(1)环加成,再用
丙酮-TsOH处理,得到四种非对映异构体3a-d的混合物,并通过制备性薄层色谱(TLC)进行了分离,确定了每种化合物的绝对立体
化学。环加合物的内(3a和3b)/外(3c和3d)比为〜11:1,3a(1 R,4 S)和3b(1 S,4 R)的比为〜3:1。Diels-Alder反应通过与
呋喃环抗或同位的1的β-糖基部分不对称诱导而发生。