Efficient Access of Heterocycles Utilizing Inherent Carbodicationic Reactivity of Ynone via Lewis Acid Catalysed C─C Triple Bond Cleavage

Divalent carbodicationic synthon has attracted significant attention due to its unique reactivity and bonding. The application of this synthon in synthetic settings is still fancy owing to its super-electrophilicity. Generation of this reactive intermediate in a catalytic fashion is challenging. For the first time, the reactivity of the chemical equivalent of divalent dication synthon has been proposed via Lewis acid-catalysed heterolytic ionisation of ynone via sequential conjugate addition to ynone followed by C─C bond cleavage to afford heteroarenes. A library of quinazolinones and 2-substituted quinazolinones has been synthesised with good to excellent yields having a wide range of functional group tolerance and broad substrate scope using 2-amino benzamides as a nucleophilic partner. Furthermore, 1,2-diaminobenzenes afforded the corresponding benzimidazole in synthetically good yield. The generality of this strategy has been demonstrated by the successful synthesis of 6-mono and 2,6-di-substituted quinazolinones and 2,4,6-tri-substituted quinazoline with very high efficiency. The mechanistic study confirmed the role of the cooperative effect and secondary orbital interaction in Grob-type fragmentation and not the involvement of any radical intermediate in the catalytic cycle.