An unprecedented N- to C-sulfonyl migration in the reaction of azomethine amine and allenoates: Access to arylsulfonylmethyl substituted pyrazolo[1,5-c]quinazoline and mechanistic studies

A serendipitous discovery of [1,3]-sulfonyl migration has been made in the two-component reaction of azomethine imine and allenoates. Current methodology involving N–S bond cleavage and C–S bond formation provided easy access to biologically important arylsulfonylmethyl substituted pyrazolo[1,5-c]quinazolines. Subsequently, a one-pot sequential protocol has been developed from the easily available starting material. The mechanistic investigation using quantum chemical methods revealed that the sulfonyl migration step is a concerted [1,3]-sigmatropic shift.