Compostos heterocíclicos estruturalmente diversos podem ser facilmente obitdos através do processo sequencial Pummerer/cicloadição/ ciclização via ion N-acilimínio.

Many structurally diverse heterocyclic compounds can be easily accessed via the domino Pummerer/cycloaddition/N-acyliminium ion cyclization cascade.

gamma-Hydroxy-alpha-diazo-beta-ketoesters are key intermediates in the chemistry of penicilin-based antibiotics and natural products. The method developed here for the synthesis of ethyl 2-diazo-4-hydroxy-3-oxo-butanoate 17 (in two steps from the diazo mercurial 2) compares very favorably with those reported in the literature for similar compounds. The Rh2(OAc)4-mediated intramolecular OH-insertion reaction of the diazo hydroxy ester 17 was investigated, furnishing the oxetan-3-one-2-carboxilate 18 in good yield. When the diazo ester lacks a free hydroxyl group as in the case of the phenoxy diazo ester 11 an intramolecular CH-insertion takes place, affording the 2H-chromene 20 in almost quantitative yield. The behavior of other functionalized diazo esters towards Rh2(OAc)4 was also investigated.

3(2H)-Furanona-2-carboxilatos têm sido preparadas em bons rendimentos e seletividade moderada (d.e. ca 60%), a partir da reação de inserção de O-H intramolecular de delta-hidroxi-alfa-diazoésteres catalisada por Rh2(OAc)4. Observou-se que as furanonas 2,5-cis substituídas são formadas inicialmente na reação, sofrendo epimerização quando submetidas à cromatografia em sílica gel, fornecendo os isômeros 2,5-trans correspondentes. A decomposição de gama-azido-delta-hidroxi-alfa-diazoestéres catalisada por Rh2(OAc)4 também forneceu 3(2H)-furanona-2-carboxilatos. Estes compostos são formados a partir de transformações sequenciais, envolvendo primeiramente uma reação de inserção de O-H intramolecular, seguido de um rearranjo sigmatrópico concertado [3,3] do intermediário alil azida.

The Rh2(OAc)4 catalyzed intramolecular O-H insertion reaction of delta-hydroxy-alpha-diazoesters affords 3(2H)-furanone-2-carboxylates in good yield but with moderate selectivity (d.e. ca 60%). The initially formed 2,5-substituted cis-furanones were found to epimerize to the corresponding 2,5-trans isomers when subjected to silica gel chromatography. The Rh2(OAc)4 catalyzed decomposition of gamma-azido-delta-hydroxy-alpha-diazoesters also furnished 3(2H)-furanone-2-carboxylates. These compounds are derived by a sequential O-H insertion reaction followed by a concerted [3,3]-sigmatropic shift of the allylic azide intermediate.