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Synthesis of thiochromenes

Recent Literature

Amidine-based catalysts, particularly homobenzotetramisole and its analogues, achieve high enantioselectivities and yields in a reagent-free catalytic transformation of α,β-unsaturated thioesters into 2-substituted thiochromenes with carbon dioxide as the only byproduct.
N. A. Ahlemeyer, V. B. Birman, Org. Lett., 2016, 18, 3454-3457.

A highly enantioselective cascade sulfa-Michael/Julia-Kocienski olefination reaction between 2-mercaptobenzaldehydes and β-substituted vinyl PT-sulfones provides a wide range of 3,4-unsubstituted 2H-thiochromenes with excellent enantioselectivities. This reaction is catalyzed by diphenylprolinol TMS ether and proceeds through an aromatic iminium intermediate.
A. K. Simlandy, S. Mukherjee, J. Org. Chem., 2017, 82, 4851-4858.

Tetramethylguanidine (TMG) promotes a cascade thiol-Michael-aldol-dehydration reaction between 2-mercaptobenzaldehyde and cinnamate esters to provide 2H-thiochromene-3-carboxylate derivatives with a variety of substituents in high yields.
T. T. H. Nguyen, T. X. Nguyen, T. T. T. Cao, T. H. Dinh, H. H. Nguyen, T. T. T. Bui, V. P. Pham, D. H. Mac, Synlett, 2017, 28, 429-432.