<i>N</i>‑Heterocyclic Carbene/Lewis Acid Dual Catalysis for the Divergent Construction of Enantiopure Bridged Lactones and Fused Indenes

The chiral triazole carbene and Ti­(OPr-i)4 cocatalyzed reaction between α,β-unsaturated aldehydes and 2-(aroylvinyl)­benzaldehydes was systematically studied. A divergence in reaction pathways was observed under different reaction conditions. In benzene solvent and at ambient temperature, the reaction produced 4,5-dihydro-1,4-methanobenzo­[c]­oxepin-3-ones, the bridged caprolactones, as the major products in moderate yields with excellent enantioselectivity. The same reaction in dichloroethane and at 50 °C, however, gave 2,8-dihydrocyclopenta­[a]­indenes as the major products in most cases. The application of the method developed was demonstrated by the transformation of the bridged lactone products into enantiopure 4-hydroxy-1,2,3,4-tetrahydronaphthalene-2-carboxylic acids.本研究系统考察了手性三氮唑卡宾（chiral triazole carbene）与四异丙氧基钛（Ti(OPr-i)4）共催化的α,β-不饱和醛与2-(芳甲酰乙烯基)苯甲醛之间的反应。不同反应条件下该反应的路径呈现显著分歧：在苯溶剂、室温条件下，反应以中等收率与优异对映选择性生成主要产物——4,5-二氢-1,4-甲烷并苯并[c]氧杂卓-3-酮，即桥联己内酯类化合物；而在二氯乙烷溶剂、50℃条件下，多数反应的主要产物为2,8-二氢环戊并[a]茚。通过将桥联内酯产物转化为对映纯的4-羟基-1,2,3,4-四氢萘-2-羧酸，验证了本开发方法的应用价值。