N-苄基-3(S)-邻苯二甲酰亚胺基-4(S)-[4(S)-2,2-二甲基-1,3-二氧环戊-4-基]-2-氧吖丁啶的合成

Synthesis of N Benzyl-3( S ) phthalimido-4( S) \[4( S) 2,2 dimethyl 1,3 dioxolan 4 yl\] 2 oxo azetidine

以Ｌ－抗坏血酸（１）为原料， 经３ 步反应制得（Ｓ）－缩异丙氧叉甘油醛（４）． 该手性醛与苄胺缩合制得相应的手性亚胺（５）． 甘氨酸经保护后制成酰氯， 在有机碱作用下首先生成不稳定的烯酮（８）， 继与手性亚胺５ 迅速进行［２＋ ２］环加成反应， 合成标题化合物Ｎ－苄基－３（Ｓ）－邻苯二甲酰亚胺基－４（Ｓ）－［４（Ｓ）－２，２－二甲基－１，３－二氧环戊－４－基］－２－氧吖丁啶． 由于环加成的面向立体选择性容易控制，

S ) Glyceraldehyde acetonide 4 which is a very useful chiral intermidiate in stereoselective synthesis was prepared conveniently by a new three step synthetic method from natural chiral resource of L ascorbic acid 1. The chiral aldehyde condensed with benzyl amine to produce adapted chiral imine 5. The imine is unstable, but it can carry a \ cyclic addition with ketene 8 which was obtained from phthalimidoacetyl chloride and triethylamine under mild conditions, and produce the title compound, N benzyl 3 (S) phthalimido 4 (S) [4(S) 2,2 dimethyl 1,3 dioxolan 4 yl] 2 oxo azetidine. Because of the high facial stereoselection in cyclic addition mechanism and attacking with ketene in unblocked face of the imine, the optical purity of the final product is quite satisfactory.