Design and Application of m-Hydroxybenzyl Alcohols in Regioselective(3+3)Cycloadditions of 2-Indolymethanols

A new class of m-hydroxybenzyl alcohols has been designed as competent three-carbon building blocks and achieved their applica-tion in 2-indolylmethanol-involved regioselective(3+3)cycloadditions under the catalysis of Br?nsted acids.By this appoach,a series of indole-fused six-membered cycloadducts have been synthesized in overall good yields(up to 98%)with excellent regioselectivity(all>95:5 rr),thus affording a powerful method for the construction of indole-fused six-membered rings.Moreover,a catalytic asymmetric version of this(3+3)cycloaddition has been preliminarily investigated,which revealed the potential of the reaction for constructing chiral indole-fused six-membered rings in an enantioselective manner.This work not only has accomplished the first design of m-hydroxybenzyl alcohols as competent reactants,but also represents the first application of m-hydroxybenzyl alcohols as three-carbon building blocks in cycloadditions.In addition,this work provides a good example for regioselective and C3-nucleophilic(3+3)cycloadditions of 2-indolylmethanols,which will substantially enrich the chemistry of 2-indolylmethanols.