Proline-based Organocatalyst for the Synthesis of Arylidene Benzofuranone Intermediates Enabling the Construction of Aurone-derived Azadienes

Organocatalysis has been recognized as a part of chemical research for a long time, and it gained significant attention in catalysis in recent decades. Amine catalyst is a substantial type of organocatalysis, and it is successively employed for the activation of carbonyl compounds. This manuscript delves into the exploration of a proline-based organocatalyst for the synthesis of arylidene benzofuranone intermediates, a critical step that facilitates the subsequent construction of aurone-derived azadienes. In this work, we successfully reported the synthesis of arylidene benzofuranone intermediates through Aldol condensation of benzofuranone with different aldehydes enabled by proline-derived organic catalysts. To achieve this strategy, six examples of amine organocatalysts (A1-A6) were evaluated to showcase the optimal catalyst for this transformation. Moreover, the arylidene benzofuranone intermediates were further employed for the synthesis of interesting aurone-derived azadiene substrates through its reaction with TsNH2. Notably, the using of organocatalyst A6 resulted in the delivery of the product with the best yield (94% isolated yield). Under the optimized conditions, different aromatic and heterocyclic containing aldehydes were effectively tolerated to generate the corresponding arylidene benzofuranone intermediates, which further converted to the azadiene products in high to excellent yield. The claimed structures were confirmed by the spectral analysis.