DielsâAlder reactions of chiral dienophiles: (2R,4S)- and (2R,4S)-2-vinyl-1,3,2-oxazaphospholidin-2-ones (3 and 4) derived from (S)-valinol with cyclopentadiene led to mixtures of endo- and exo-adducts with high diastereofacial selectivity (>90% for 3 and 80 and 88% respectively for 4); an explanation is proposed based on X-ray crystallographic structures for the dienophile and the derived endo-cycloadduct 5.
手性二烯亲体的Diels–Alder反应:(2R,4S)-和(2R,4S)-2-
乙烯基-1,3,2-氧杂膦烯-2-酮(3和4)是由(S)-valinol与
环戊二烯反应得到的,生成了具有高二面体选择性的内烯和外烯加成物(3的选择性超过90%,4分别为80和88%);根据二烯亲体和衍生的内烯加成物5的X射线晶体结构,提出了一种解释。