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Ring-Forming Thioboration of C–C π-Bonds
Catalyst-Free Formal Thioboration to Synthesize Borylated Benzothiophenes and Dihydrothiophenes.
Angew. Chem. Int. Ed. 2016;
19 December 2016 (online)
Blum and co-workers developed a catalyst-free formal thioboration to produce borylated benzothiophenes and dihydrothiophenes in good to high yields.
The authors propose a reaction mechanism in which a boron-induced activation of the alkyne is followed by electrophilic cyclization to generate the borylated benzothiophene after demethylation of the sulfonium intermediate. Boron acts here as a carbophilic Lewis acid.