Construction of 3-Methyl-2-Substituted Benzo[<i>b</i>]furans and 3-Methyl-2-Substituted Benzo[<i>b</i>]thiophenes Using Solid Calcium Carbide as a Substitute for Gaseous Acetylene
Zhiqiang Wang, Zhenrong Liu, Ting Shao, Zheng Li
Abstract
A concise method for the facile construction of 3-methyl-2-substituted benzo[ b ]furans and 3-methyl-2-substituted benzo[ b ]thiophenes using low-cost, abundant, and easy-to-use solid calcium carbide instead of flammable and explosive gaseous acetylene as an original alkyne source, o -bromophenyl ethers or o -bromophenyl thioethers as substrates through an intramolecular carbanion-yne cyclization in a 5- exo-dig manner, and subsequent double-bond isomerization is described. The simultaneous formation of two C–C bonds is realized in a one-step route. The wide substrate scope, high yield, and simple workup manipulations are also merits of this method. The synthetic strategy can also be suitable for the gram scale.