A novel tandem [4++2] cycloaddition–elimination reaction of 4,4-dimethyl-2-styryl-1,3-oxathianes with olefins

A novel tandem [4++2] cycloaddition–elimination reaction of 1,3-oxathianes 1a,b with olefins promoted by titanium tetrachloride to give 3,4-dihydro-2H-thiopyrans 3 was developed. 4,4-Dimethyl-2-styryl-1,3-oxathiane (1a) was used as a synthetic equivalent of a highly reactive thiocinnamaldehyde. Geminal dimethyl substituents at the 4-position of 1,3-oxathianes 1 are an intrinsic part of this cycloaddition–elimination reaction.