ORGN 402

Recently we reported synthesis of a mixture of 5,6-dihydro-4H-thieno[3,2-b]pyrrol-5-ones 2 and the corresponding enols 3 from the reactions of 3-(3-alkylamino-5-arylthieno-2-yl)-2-diazo-3-oxopropanoates 1 (R²=H, R³=alkyl) with Rh₂(OAc)₄•2H₂O (catalyst) in PhH at reflux.¹ On the other hand, we have found that on heating compounds 1 (R²=CO₂R, R³=Me) in the presence of Rh₂(OAc)₄•2H₂O (catalyst) under the same foregoing conditions gave dihydrothieno[3,2-b]pyridones 4. Interestingly, the reactions of 1 (R²=CO₂R, R³=Me) in the presence of Rh₂(CF₃CF₂CF₂CO₂)°©₄ (catalyst) in CH₂Cl₂ at rt gave compounds 5 (80 - 92%). Treatment of 1 (R²=CO₂Et, R³=Me) with Rh₂(OAc)₄•2H₂O (catalyst) in a mixture of PhH and MeOH (10 : 1, v/v) at reflux gave compounds 4 (R=R¹ =Et), 6, and 7. The CO₂Et group at position 6 of compound 7 is envisaged to originate from the nitrogen atom of the carbamate functionality of 1. Mechanism for the migration of CO₂Et group will be discussed.