Diazo transfer reactions of tosyl azide with carbocyclic β-keto esters: production and decomposition of ring-opened N-tosylcarbamoyl-substituted α-diazo esters

Abstract

The diazo transfer reaction of tosyl azide 1 with methyl 2-oxocyclopentanecarboxylate 2a, ethyl 2-oxocyclohexanecarboxylate 2b and methyl 2-oxocycloheptanecarboxylate 2c, in the presence of triethylamine, gives ring-opened diazo amido esters 3a–c in fairly high yields. Similar reaction with ethyl 2-oxocyclooctanecarboxylate 2d and methyl camphor-3-carboxylate 2e also leads to the respective diazo esters 3d,e but accompanied by the corresponding azido transfer products 6, 7 to a significant (or major) extent. The thermal, photochemical and rhodium(II) acetate-catalysed decomposition of the novel diazocarbonyl compounds 3a–e has been examined. The results show that intramolecular cyclization onto the N-tosylcarbamoyl substituent can smoothly take place provided that it gives rise to a six-membered ring ylide or diazonium betaine intermediate. Otherwise, β-hydride elimination by an intermediate carbene or rhodium-carbenoid becomes the preferred, if not exclusive, decomposition mode. However, unusual behaviour is encountered with the diazo amido ester 3d in that its rhodium(II)-induced decomposition results in the preferential formation of the α-hydroxy ester 19.