Chemoselective oxidation of benzophenazines by m-CPBA: n-oxidation vs. oxidative cleavage

• Autor(a) principal: Silva,Raphael S. F.
• Data de Publicação: 2007
• Outros Autores: Amorim,Mauro B. de, Pinto,Maria do Carmo F. R., Emery,Flávio S., Goulart,Marília O. F., Pinto,Antonio V.
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Journal of the Brazilian Chemical Society (Online)
• Texto Completo: http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532007000400014
• topic: m-CPBA oxidation; phenazines; chemoselectivity; N-oxides; macrolactones; oxidative cleavage

Chemoselectivity is observed when a pyran-benzo[a]phenazine and a furan-benzo[a]phenazine from beta-lapachone and nor-beta-lapachone, respectively, were submitted to oxidation by m-CPBA. The pyran phenazine furnished mainly macrolactones, while the furan one led exclusively to a phenazine N-8 oxide. To understand this difference in reactivity, we synthesized a new furan phenazine, with the reactive double bond site less hindered than that of the derivative from nor-beta-lapachone. This furan phenazine, upon oxidation with m-CPBA, furnished mainly the expected macrolactone. These experimental results, along with preliminary analysis based on mechanical molecular calculations of the ground state of the substrates, allowed us to suggest that the observed chemoselectivity has a steric oxidant approach control origin, related to the presence of the geminal methyl groups in the phenazine structure. Several of the synthesized compounds are, herein, reported for the first time.