Zou W, Wang Z, Lacroix E, Wu S H, Jennings H J
Institute for Biological Sciences, National Research Council of Canada, Ottawa, Ontario, Canada K1A 0R6, Canada.
Carbohydr Res. 2001 Aug 30;334(3):223-31. doi: 10.1016/s0008-6215(01)00187-2.
Base treatment of O-benzyl protected C-2- or C-4-ulopyranosyl compounds (4 alpha, 4 beta, and 11) by either 10% Et(3)N or 1% K(2)CO(3) in MeOH initiated a beta elimination to afford alpha,beta-unsaturated C-ulopyranosyl compounds (5 alpha, 5 beta, and 12), which further rearranged in a stereocontrolled manner to multifuctionalized alpha,beta-cyclopentenones (6 and 14) in 70-80% yield. Both C-alpha- and C-beta-2-ulosides (5 alpha and 5 beta) produced the same cyclopentenone 6, indicating that a 1,2-enolate is formed prior to the cleavage of the C-5--O bond. Because 6 is racemic, it was probably formed by the intramolecular cycloaldolization of two equally populated enantiomeric intermediates. When treated with 90% Et(3)N in MeOH, 5 alpha yielded almost exclusively 15 (isomer of 6), which was formed by a migration of the double bond in 5 alpha during the previously described rearrangement. Thus either 6 or 15 was the major product, depending on the base used.
用10%的三乙胺或1%的碳酸钾在甲醇中对O-苄基保护的C-2-或C-4-吡喃戊糖基化合物（4α、4β和11）进行碱处理，引发β消除反应，得到α,β-不饱和C-吡喃戊糖基化合物（5α、5β和12），这些化合物进一步以立体控制的方式重排为多官能化的α,β-环戊烯酮（6和14），产率为70-80%。C-α-和C-β-2-戊糖苷（5α和5β）都生成了相同的环戊烯酮6，这表明在C-5-O键断裂之前形成了1,2-烯醇盐。由于6是外消旋体，它可能是由两种等量的对映体中间体的分子内环醇缩合形成的。当在甲醇中用90%的三乙胺处理时，5α几乎只生成15（6的异构体），它是由5α中的双键在上述重排过程中迁移形成的。因此，根据所用的碱不同，6或15是主要产物。
