Facile Synthesis of Stable Analogues of 2-Oxocyclobutanecarboxylates: 2-cyclobutanecarboxylates, Derivatives, and Reactions

Article abstract of DOI:10.1021/jo00075a047

An efficient two-step synthesis of 2-<(diphenylmethylene)amino>cyclobutenecarboxylate (4a) and some analogous derivatives from 2-chloro-2-cyclopropylideneacetates 2, 17, 22, and 25 and nonenolizable ketimines, especially diphenylmethyleneamine (DPMA-H), is described.A likely mechanism for the formation of 4a from the primary Michael adduct 3 of DPMA-H to 2 and its substuituted analogues is presented.The unique neighbouring group effect of the DPMA moiety to allow formation of an azaspiropentane intermediate and its regioselective rearrangement to cyclobutenaminederivatives is discussed and further exemplified by an extremely facile SET α-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 transesterification, hydrolysis to methyl 2-oxocyclobutanecarboxylates, and addition of N-phenyltriazolinedione.