Reactions of β-styrylmalonates with aromatic aldehydes: the development of a catalytic version using gallium trichloride

A catalytic system based on gallium trichloride and silver tetrafluoroborate was successfully tested in the [2 + 3]-annulation reaction of β-styrylmalonates with aromatic aldehydes leading to 2-arylinden-1-ylmalonates. This allows to reduce the amount of gallium compound and to halve the amount of aldehyde used while maintaining the optimal yields of the resulting indenylmalonates previously achieved using 2 equiv. of GaCl₃ and 4–6 equiv. of aldehyde. Under these conditions, aldehydes previously non-reactive were also involved into the transformation.