LIGAND EFFECTS IN THE RHODIUM(II)-CATALYZED REACTIONS OF ALPHA-DIAZOAMIDES - OXINDOLE FORMATION IS PROMOTED BY THE USE OF RHODIUM(II) PERFLUOROCARBOXAMIDE CATALYSTS

An improved procedure for the preparation of ethyl 2-diazomalonyl chlo ride ws developed which involves the reaction of ethyl diazoacetate wi th triphosgene. Using this diazo acid chloride, it was possible to pre pare a variety of diazoamides from substituted amines. The rhodium(II) -catalyzed decomposition of these diazoamides was studied in order to probe the chemoselectivity of the carbenoid intermediates in intramole cular insertion reactions. Rhodium(II) acetate decomposition of N-benz yl-2-diazo-N-phenylmalonamic acid ethyl ester resulted in intramolecul ar C-H insertion to give ethyl 1,4-diphenyl-2-oxoazetidine-3-carboxyla te. By changing the catalyst ligand to trifluoroacetamide, beta-lactam formation was completely suppressed in favor of the aromatic C-H inse rtion which produces an oxindole as the only detectable product. The c ompetition between aliphatic and aromatic carbon-hydrogen insertion of 2-diazo-N-phenylmalonamic acid ethyl ester provides another example o f ligand effectiveness in controlling chemoselectivity in dirhodium(II )-catalyzed metal carbene reactions. Thus, treatment of the N-isobutyl diazoanilide with rhodium(II) acetate results in exclusive aliphatic C -H insertion giving ,4-dimethyl-2-oxo-1-phenylpyrrolidine-3-carboxylic acid ethyl ester, while the perfluorobutyramide ligand promotes oxidi nole formation by aromatic C-H insertion. Several other rhodium(II)-ca talyzed reactions were studied and were found to be highly catalyst de pendent, rhodium(II) perfluorocarboxamides promoting aromatic C-H inse rtion, and hence oxindole formation, over O-H insertion, cyclization o nto adjacent triple bonds, or cyclization to generate 1,3-dipolar inte rmediates.