title: Synthesis of highly substituted γ-butyrolactones by a gold-catalyzed cascade reaction of benzyl esters.
abstract: Easily accessible benzylic esters of 3-butynoic acids in a gold-catalyzed cyclization/rearrangement cascade reaction provided 3-propargyl γ-butyrolactones with the alkene and the carbonyl group not being conjugated. Crossover experiments showed that the formation of the new C-C bond is an intermolecular process. Initially propargylic-benzylic esters were used, but alkyl-substituted benzylic esters worked equally well. In the case of the propargylic-benzylic products, a simple treatment of the products with aluminum oxide initiated a twofold tautomerization to the allenyl-substituted γ-butyrolactones with conjugation of the carbonyl group, the olefin, and the allene. The synthetic sequence can be conducted stepwise or as a one-pot cascade reaction with similar yields. Even in the presence of the gold catalyst the new allene remains intact.
authors.affiliation: Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg (Germany), Fax: (+49) 711-685-4205.
authors.forename: Maria Camila
authors.initials: MC
authors.lastname: Blanco Jaimes
authors.forename: Alexander
authors.initials: A
authors.lastname: Ahrens
authors.forename: Daniel
authors.initials: D
authors.lastname: Pflästerer
authors.forename: Matthias
authors.initials: M
authors.lastname: Rudolph
authors.forename: A Stephen K
authors.initials: AS
authors.lastname: Hashmi
keywords: alkynes; allenes; furans; gold; lactones