作者:Daniela Hendea、Sabine Laschat、Angelika Baro、Wolfgang Frey
DOI:10.1002/hlca.200690181
日期:2006.9
N-Boc-protected L-proline (6) was converted into the bicyclic lactim ether (8aS)-6,7,8,8a-tetrahydro-1-methoxypyrrolo[1,2-a]pyrazin-4(3H)-one (5) in four steps (Scheme 1). Deprotonation with LDA or LHMDS and subsequent alkylation resulted in the diastereoisomeric products cis- and trans-9. The diastereoselectivity was mainly dependent on the electrophile. Whereas small alkyl halides gave preferably
N - Boc保护的L-脯氨酸(6)被转化为双环内酰胺醚(8a S)-6,7,8,8a-四氢-1-甲氧基吡咯并[1,2 - a ]吡嗪-4(3 H) -在四个步骤(方案1)中分配一个(5)。去质子与LDA或LHMDS和随后烷基化导致非对映异构产品顺-和反式- 9。非对映选择性主要取决于亲电试剂。较小的烷基卤化物优选为cis - 9,而空间上要求更高的烷基卤化物则产生顺式/反式混合物。亲电轴承π -System青睐反式-产品9。一些分离的顺式-和反式-lactim醚9被转化成相应的二酮哌嗪的顺式-和反式- 10通过酸水解。几种化合物的结构和构型已通过NMR和NOE实验以及X射线晶体学证实(图1-4)。