Reactions of dimethoxycarbene with dimethyl 2,3-dicycanomaleate and fumarate.

Dimethoxycarbene, in 2-fold or larger excess, reacts with dimethyl 2,3-dicyanomaleate and fumarate to afford an unstable dihydrofuran 1:1 adduct that was shown to react further with the carbene to afford a 2:1 adduct reported previously. In an astonishing process, the dihydrofuran reacts with water to afford a mixture of (d,l and meso) dimethyl 2,3-dicyanosuccinates in which both hydrogen atoms of water were used to hydrogenate a C=C bond.