Redox deracemization of 1,3,4,9-tetrahydropyrano[3,4-b]indoles†
The existing asymmetric synthesis of enantiopure α-substituted cyclic ethers predominantly relies on the enantioselective C–C bond formation involving a prochiral oxocarbenium ion intermediate. In such a strategy, enantioselectivity and efficiency are typically susceptible to the electronic and substituent effects of either nucleophile or electrophile partners. Here, we describe a strategically different redox deracemization of α-substituted 1,3,4,9-tetrahydropyrano[3,4-b]indoles. This method exhibits good compatibility with the regional variation of the electronic or substituent effect of substrates, thus providing a practical and efficient supplement to the traditional strategy.