Rhodium(II)-catalyzed intramolecular carbonyl ylide formation of α-diazo-β-ketoesters derived from N-phthaloyl-α-amino acids

Abstract

Starting from L-alanine, L-phenylalanine, L-leucine, L -norleucine, or L-isoleucine, 2-diazo-3-oxo-4-phthalimido-alkanoates 8 were prepared in three steps. Considerable racemization occurred at the stage of the 3-oxo-4-phthalimido-alkanoates 7. Dirhodium tetraacetate effectively catalyzed the intramolecular formation of carbonyl ylides 9, which in the absence of a trapping reagent underwent a [3+3] cycloaddition reaction to form the dimers 10. Carbonyl ylides 9 underwent [3+2] cycloaddition reactions with several electron-deficient alkenes and alkynes to give oxygen and nitrogen containing multicyclic systems 12-16. The keto group of the αoxy-β-ketoester moiety of cycloadducts 2 and 12 is easily hydrated to give the gem-diol. ©ARKAT-USA, Inc.