title: Palladium(0)-catalyzed synthesis of medium-sized heterocycles by using bromoallenes as an allyl dication equivalent.
abstract: We have developed a highly regio- and stereoselective synthesis of medium-sized heterocycles containing one or two heteroatoms via cyclization of bromoallenes bearing an oxygen, nitrogen, or carbon nucleophilic functionality in the presence of a palladium(0) catalyst and alcohol. In this reaction, bromoallenes act as an allyl dication equivalent, and the intramolecular nucleophilic attack takes place exclusively at the central carbon atom of the allene moiety. Interestingly, bromoallenes having a carbon nucleophile with a five-atom tether afford eight-membered rings with trans-configuration, while those having an oxygen or a nitrogen nucleophile give the corresponding cis-rings selectively. This is the first example that demonstrates the synthesis of medium-sized rings via cyclization of bromoallenes, and this reaction provides a very useful method for a catalytic synthesis of seven- and eight-membered heterocycles without using high dilution conditions.
authors.affiliation: Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka, Suita, Osaka 565-0871, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Ohno
authors.forename: Hisao
authors.initials: H
authors.lastname: Hamaguchi
authors.forename: Miyo
authors.initials: M
authors.lastname: Ohata
authors.forename: Shohei
authors.initials: S
authors.lastname: Kosaka
authors.forename: Tetsuaki
authors.initials: T
authors.lastname: Tanaka