An approach to the construction of the carbon skeleton of marine nor-sesquiterpenes. Total synthesis of (±)-dehalo-napalilactone

• Autor(a) principal: Diaz,Gaspar
• Data de Publicação: 2001
• Outros Autores: Coelho,Fernando
• 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=S0103-50532001000300007
• topic: nor-sesquiterpene; napalilactone; marine natural products; dehalo-napalilactone; pathylactone

We disclose herein a synthetic approach for the preparation of an unusual carbon skeleton, which was found in nor-sesquiterpenes isolated from marine corals. The main structural feature of this skeleton is the presence of two contiguous quaternary centers, one of them bears a spiro gamma-butyrolactone moiety. One of the quaternary centers was prepared with moderate stereoselectivity by the conjugate addition of lithium dimethylcuprate to 2-methylcyclohexenone, followed by the trapping of the intermediate enolate with allyl bromide to furnish trans-2-allyl-2,3-dimethylcyclohexan-2-one, as a major diastereoisomer. The preparation of the quaternary centers bearing the spiro gamma-butyrolactone moiety was secured by the addition of a suitably functionalized organolithium reagent on trans-2-allyl-2,3-dimetylcyclohexan-2-one, followed by separation of the isomers and two oxidation steps. This strategy has permitted us to report the racemic total synthesis of a non-natural nor-sesquiterpene derivative, in 6 steps and 16% overall yield, from 2-methylcyclohexenone.