Efficient One-Pot Synthesis of Dithieno(dibenzothieno)-Fused Cycloheptanones, Tropones, and Cyclooctanones.

The reactions of alpha,beta-unsaturated amide/triflic anhydride complexes (generated in situ from the corresponding amides and triflic anhydride) with dithiophenes and dithienylmethanes proceed as tandem alkylation-Vilsmeier-Haack acylation to form dithieno- and dibenzothieno-fused cycloheptanones and cyclooctanones in moderate to good yields. The reactions of 2-bromo-N,N-dimethylacrylamide/triflic anhydride complex allow preparation of tropones in a simple one-pot procedure. The reaction of 2,2-dibenzothienylmethane with dimethylacrylamide/triflic anhydride complex proceeds unusually to afford dimethylaminonaphthalene in addition to the predictable fused cyclooctanone.