Benzo thiophene, Diels-Alder reactions synthesis

Diels-Alder reactivity of thiophene and benzothiophene remains poorly understood. AMI semiempirical studies examining the activation of thiophene for this thermally allowed [4+2] cycloaddition process have shown that the usual synthesis approaches (use of highly reactive dienophiles, substitution on thiophene, increased reaction pressures) have only small effects on rate enhancement. However, use of the corresponding S-methylthiophenium salts, which have little aromaticity, should provide excellent activation for Diels-Alder reactions of thiophenes even with poor dienophiles such as ethylene <95JHC483>. This AMI approach has been applied to examine Diels-Alder reactions of benzo[6] and benzo[c]thiophenes the theoretical data agree with experimental results <95JCS(P1)1217>. 

Benzo[6]thiophene, 3-pyrrolidino-cycloaddition reactions, 4, 789 Benzo[6]thiophene, 4,5,6,7-tetrafluoro-electrophilic substitution, 4, 797 synthesis, 4, 895, 932 Benzothiophene, tetrahydro-synthesis, 4, 908 Benzo[6]thiophene, vinyl-cycloaddition reactions, 4, 794 Diels-Alder reactions, 4, 908 Benzo[e]thiophene, 1 -alkenyl- 1,3-dihydro-... 

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