Copper(II) in organic synthesis. VI1 reaction of the copper(II) acetate complex of 1-methylisatin-3-chlorophenylhydrazone with dimethyl acetylenedicarboxylate

The copper(II) complex of 1-methylisatin-3-p-chlorophenyl hydrazone (2) reacted with dimethyl acetylenedicarboxylate (DMAD) in accordance to two reaction pathways. Oxidation performed by Cu++ gave 1-methyl-3-carbenindolin-2-one (12), trapped by DMAD to give products 3-5, and p-chlorophenylradical (13), trapped either by DMAD to give 6, or by the free ligand 1 to give 7 or by carbenindolinone and DMAD to give 8. The second pathway involved a [2+2] cycloaddition followed by electrocyclic ring opening and intramolecular cyclization to give 1-methyl-2-indolinone-3-spiro-5'-1'-p-chlorophenyl-3', 4'-dimethoxycarbonyl-2'-pyrazoline (9) whose structure and configuration were demonstrated by an independent synthesis.