An Efficient Protocol for the Synthesis of Dibenzodithiapentalene

Significance

Reported is the improved synthesis of dibenzodithiapentalene (6) employing an S_NAr approach. Directed ortho metalation of 1 followed by oxidative dimerization using PhNO₂ afforded the desired biaryls 2 and 3 in good yield. Subsequent acidic deprotection gave the diol 4 and dithiol 5, ready for the final cyclizations. Exposure of dithiol 5 to standard S_NAr conditions (Cs₂CO₃, DMSO, high temperature) led smoothly to the desired pentalene in an impressive yield. However, when diol 4 was subjected to similar reaction conditions, none of the desired product was obtained. Instead, intermolecular condensation produced macrocyclic 8 as the major product.