Uncatalysed (thermal) and Lewis acid-promoted asymmetric hetero-Diels–Alder reaction of 1-thiabuta-1,3-dienes (thiochalcones) with di-(–)-menthyl fumarate. Configuration determination by X-ray crystallographic analysis of (2S,3R,4R)-(+)-2,3-bis[(–)-menthoxycarbonyl]-4,6-diphenyl-3,4-dihydro-2H-thiopyran and conversion of cycloadducts into optically pure diols
作者:Takao Saito、Hironari Fujii、Satoshi Hayashibe、Teruki Matsushita、Hideo Kato、Kimiko Kobayashi
DOI:10.1039/p19960001897
日期:——
1-Thiabuta-1,3-dienes 1 (thiochalcones) underwent asymmetric hetero-Diels–Alder reaction with di-(–)-menthyl fumarate 2 to afford a mixture of 3,4-cis-(3 and 4) and 3,4-trans-dihydrothiopyrans (5 and 6) in good-to-excellent chemical yield with fair diastereoselectivities, the stereoisomer 3 predominating. An endo(3,4-cis): exo(3,4-trans) selectivity was observed in the ratio 98–85:2–15. The uncatalysed
1-Thiabuta-1,3-dienes 1(thiochalcones)与富马酸二(-)-薄荷基酯2进行不对称的杂Diels-Alder反应,得到3,4-顺式-(3和4)和3的混合物, 4-反式-二氢硫代吡喃(5和6)的化学收率非常好,非对映选择性很好,立体异构体3占主导地位。以98-85:2-15的比例观察到内切(3,4-顺式):外切(3,4-反式)选择性。在20–40°C时未催化的反应显示非对映体π面选择性为10–48%de,而在适当的反应条件下使用合适的路易斯酸可使选择性提高到62–71%de。3,4-顺式-在热反应和路易斯酸促进的反应中均有利地形成的-立体异构体,具有相同的构型2 S,3 R,4 R(3)。通过使用异构体3a(R 1= R 2= Ph)的X射线晶体结构分析明确地确定了构型。可以通过色谱法和重结晶在立体化学上均质的异构体3通过LiAlH 4还原连续转化为光学纯的二醇7和8或9