Michael Addition‐Elimination and [4+1] Annulation of Sulfonylphthalide with Hydroxychalcones for the Synthesis of Alkylidenephthalides and Indanediones

A protocol for the stereoselective synthesis of alkylidenephthalides and indanediones has been developed through the reaction of o‐hydroxychalcones and their styrenyl analogues, respectively, with 3‐sulfonylphthalide. The mechanism for the former synthesis involves Michael addition‐E2 elimination sequence, while the latter involves a [4+1] Hauser‐Kraus annulation. The mechanistic studies reveal that the strategically positioned phenolic group plays a pivotal role in the observed reactivities. The alkylidenephthalides, which are latent 1,4‐dicarbonyl compounds, were further converted to triarylfurans under Paal‐Knorr conditions in good to excellent yields. This protocol unravels several key features such as substrate specific product formation, namely, alkylidenephthalides from chalcones, and indanediones from vinylogous chalcones in their reaction with 3‐sulfonylphthalide as well as the role of alkylidenephthalides as 1,4‐dicarbonyl surrogates in Paal‐Knorr furan synthesis. A stereoselective synthesis of alkylidenephthalides through Michael addition‐elimination has been demonstrated by employing 3‐sulfonylphthalide and o‐hydroxychalcones. Interestingly, the conjugated styrenyl o‐hydroxychalcones afforded unsymmetrical indanediones through [4+1] Hauser‐Kraus annulation. The strategically located phenolic group plays a pivotal role in controlling the reaction pathways. The alkylidenephthalides which are latent 1,4‐dicarbonyl compounds were further transformed into triarylfurans in good to excellent yields under Paal‐Knorr conditions.