Three-component synthesis of functionalized 5-oxo-4,5-dihydroindeno[1,2-b]pyrans.

Protonation of the reactive intermediates produced in the reaction between alkyl(aryl) isocyanides and dialkyl acetylenedicarboxylates by indan-1,3-dione leads to vinylnitrilium cations, which undergo carbon centered Michael type addition with the conjugate base of the CH-acid to produce functionalized 5-oxo-4,5-dihydroindeno[1,2-b]pyrans.