FACILE SYNTHESIS OF STABLE ANALOGS OF 2-OXOCYCLOBUTANECARBOXYLATES - [(DIPHENYLMETHYLENE)AMINO]CYCLOBUTENECARBOXYLATES, DERIVATIVES, AND REACTIONS

An efficient two-step synthesis of 2-[(diphenylmethylene)amino]cyclobu tenecarboxylate (4a) and some analogous derivatives from 2-chloro-2-cy clopropylideneacetates 2, 17, 22, and 25 and nonenolizable ketimines, especially diphenylmethyleneamine (DPMA-H), is described. A likely mec hanism for the formation of 4a from the primary Michael adduct 3 of DP MA-H to 2 and its substituted analogues is presented. The unique neigh boring group effect of the DPMA moiety to allow formation of an azaspi ropentane intermediate and its regioselective rearrangement to cyclobu tenamine derivatives is discussed and further exemplified by an extrem ely facile SET alpha-chlorination. Compound 4a and derivatives undergo a thermal ring-opening reaction to the corresponding butadienes with subsequent formation of 1,3-disubstituted 3,4-dihydroisoquinolines 39. Further transformations of 4a and some derivatives include transester ification, hydrolysis to methyl 2-oxocyclobutanecarboxylates, and addi tion of N-phenyltriazolinedione.