Ritter reactions. Part 11. The diverse reactivity of 5,10-(azenometheno)-5H-dibenzo[a,d]cyclohepten-11-yl amides with dimethyl acetylenedicarboxylate

Abstract

Each of the 5,10-(azenometheno)-5H-dibenzo[a,d]cyclohepten-11-yl amide derivatives 8a–c reacts with dimethyl acetylenedicarboxylate (DMAD) through its imine group to yield novel and unexpected heterocyclic products. Imine 8a undergoes 1:1 addition to give the conjugated enamine 10, or 1:2 addition yielding the cyclobutyl tetraester 11, depending on the conditions employed. In contrast, imine 8b undergoes addition of both DMAD and methanol affording the orthoester 12, while imine 8c is converted into the unsaturated lactam 14. Tentative mechanistic explanations for these diverse and unpredictable reactions are provided. These are supported by X-ray crystal structures of compounds 8c, 11, 12 and 14. Tetraester 11 was isolated as its inclusion compound (11)·(C₆H₆)_0.5 and the host–guest interaction involved therein are analysed in crystal engineering terms.