Catalytic Availabilities of Lewis Acidic SnCl<sub>2</sub>: Ph<sub>3</sub>PAuCl-SnCl<sub>2</sub>Composite Catalyzed Successive<i>ortho</i>-Alkenylation/O-Alkenylation of Phenols Followed by Cyclization to 1-Benzopyrans
Ph3PAuCl and SnCl2, catalyzed the formation of 1-benzopyrans from phenols and phenylacetylene. The Ph3PAuCl–SnCl2 composite catalyzed reaction was presumed to proceed through the successive ortho-alkenylation and O-alkenylation of phenols with phenylacetylene followed by cyclization of the prepared ortho- and O-dialkenylated phenol derivatives. Conveniently, all reactions with Ph3PAuCl–SnCl2 composite