Rhodium Catalyzed Synthesis of Benzopyrans via Transannulation of N-Sulfonyl-1,2,3-triazoles with 2-Hydroxybenzyl Alcohols

An efficient and novel rhodium-catalyzed transannulation of N-sulfonyl-1,2,3-triazoles with in situ generated o-quinone methides ( o-QMs) from 2-hydroxybenzyl alcohols has been achieved for the synthesis of substituted benzopyrans in good yields. The developed reaction involves nucleophilic attack of o-QM to α-imino rhodium carbenoid to generate a carbonyl ylide followed by 6π-electrocyclization and isomerization. Furthermore, the utility of the methodology was demonstrated in the one-pot synthesis and construction of polyheteroaromatics.