Efficient Access of Heterocycles Utilizing Inherent Carbodicationic Reactivity of Ynone via Lewis Acid Catalysed C─C...

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.