Unexpected σ bond rupture during the reaction of N-methyl-1,2,4-triazoline-3,5-dione with acenaphthylene and indene.

The reaction of N-methyl-1,2,4-triazoline-3,5-dione (MeTAD) with acenaphthylene and indene leads not only to the formation of the expected [2 + 2] diazetidine cycloadducts but also to unexpected 2:1 adducts of MeTAD with substrate. The structures of the products derived from acenaphthylene were confirmed by X-ray crystallography. A similar distribution of products was afforded from indene.