Rhodium-Catalyzed Enantioselective [4+2] Cycloadditions of Vinylcarbenes with Dienes

The reaction of 2-siloxycyclo-1,3-dienes with E-vinyldiazoacetates in the presence of the bulky chiral dirhodium tetracarboxylate catalyst, Rh₂(R-p-PhTPCP)₄ results in an enantioselective 4+2] cycloaddition, in which three new stereogenic centers are formed. The 4+2] cycloadducts are generated as single diastereomers with high enantiocontrol (95–98 % ee). When the diene contains an additional stereogenic center, effective kinetic resolution can be achieved.