A highly efficient and versatile strategy has been developed for the synthesis of 3-brominated thioflavonoids and benzothiophenes from readily available alkynes by using tetrabutylammonium bromide (TBAB) as the bromine source. This transformation proceeds smoothly via photocatalyzed, regioselective bromination/cyclization under metal- and additive-free conditions, with excellent functional group tolerance. This protocol enables the efficient construction of biologically relevant brominated heterocycles in up to 99% yield for 37 examples, thus offering a valuable protocol for directly introducing bromine into diverse thioflavonoids and benzothiophenes.
Yang et al. (Wed,) studied this question.