An isothiourea-catalyzed asymmetric formal [4 + 2] cycloaddition of in situ generated azoalkenes with C1 ammonium enolates

An efficient isothiourea-catalyzed stereoselective formal [4 + 2] cycloaddition of α-chloro cyclic hydrazones with carboxylic acids has been developed. Under mild conditions, a series of functionalized 4,4a,5,6-tetrahydrobenzo[h]cinnolin-3(2H)-one derivatives with two consecutive stereocenters were obtained in high yields with excellent diastereo- and enantioselectivities (up to >99% ee).