Quantitative regio-selective Diels–Alder reaction of an unsymmetrical 1,4-dithiin and anthracene through heterogeneous solid state conversion

The solid state, Diels–Alder reaction of an unsymmetrical 1,4-dithiin and anthracene produced an adduct regioselectively via a charge-transfer complex crystal prearranged to undergo a transformation among a constitutional isomeric mixture generated in the reaction solution. The heterogeneous solid state conversion allowed the reaction to proceed in almost quantitative yield.