Polarized Ketene Dithioacetals; 53:¹ A Facile Synthesis of 2-Aryl-6-methylthio-4H-pyran-4-ones and a Novel Cycloaromatization Reaction

A facile route to hitherto unreported 2-aryl-6-methylthio-4H-pyran-4-ones 4a-f has been developed by base-catalyzed condensation of acylketene dithioacetal 2 with substituted methyl benzoates 1a-f followed by subsequent ring closure of resulting α-aroylacylketene dithioacetals 3a-f. Acylketene dithioacetal 2 and the corresponding β-methylthioenone 9 are shown to undergo self-condensation and aromatization in the presence of sodium hydride and methylbenzoate in refluxing xylene to give 2, 6-bis(methylthio)-4-hydroxy-acetophenone (6) and 4-hydroxyacetophenone (10) respectively in good yields. A mechanistic pathway for the formation of 6 and 10 via 3 has been described.