Facile Synthesis of 2,5-Disubstituted Thiazoles from Terminal Alkynes, Sulfonyl Azides, and Thionoesters

A sequential procedure for the synthesis
of 2,5-disubstituted thiazoles
from terminal alkynes, sulfonyl azides, and thionoesters is reported.
A copper­(I)-catalyzed 1,3-dipolar cycloaddition of terminal alkynes
with sulfonyl azides affords 1-sulfonyl-1,2,3-triazoles, which then
react with thionoesters in the presence of a rhodium­(II) catalyst.
The resulting 3-sulfonyl-4-thiazolines subsequently aromatize into
the corresponding 2,5-disubstituted thiazoles by elimination of the
sulfonyl group.