One-Pot Synthesis of Functionalized Spirobenzofuranones via MCR involving 3-Cyanochromones

Another aspect concerning chromone chemistry leading
to the one-pot
synthesis of functionalized novel spirobenzofuranones has been described.
The synthesis involves reaction of the zwitterionic intermediates
formed by the 1:1 interaction between isocyanides and acetylenecarboxylates
with 3-cyanochromones, whereupon through an unexpected and unprecedented
reaction of the chromone moiety the isolated benzofuranones are formed.
The regioselectivity of the reaction was investigated by DFT calculations.
The geometries of the intermediates, transition structures, and intermediate
products, leading to the final products, were optimized using the
B3LYP functional with the 6-31G­(d) basis set. The structures of the
products were elucidated by 1D and 2D NMR experiments. Full assignment
of all 1H and 13C NMR chemical shifts has been
achieved. A plausible mechanistic rationale is proposed.