Gold-catalyzed annulations of 2-alkynyl benzaldehydes with vinyl ethers: synthesis of dihydronaphthalene, isochromene, and bicyclo[2.2.2]octane derivatives.
With the suitable selection of a gold catalyst as well as the appropriate control of the reaction conditions, various new gold-catalyzed cyclizations of 2-alkynyl benzaldehyde with acyclic or cyclic vinyl ethers have been developed. Acetal-tethered dihydronaphthalene and isochromenes were obtained from the reactions of 2-alkynyl benzaldehydes with acyclic vinyl ethers under mild conditions. And, more interestingly, the gold-catalyzed reactions of 2-alkynyl benzaldehyde with a cyclic vinyl ether afforded the bicyclo[2.2.2]octane derivative involving two molecules of cyclic vinyl ethers. These products contain interesting substructures that have been found in many biologically active molecules and natural products. In addition, a gold-catalyzed homo-dimerization of 2-phenylethynyl benzaldehyde 1a was observed when the reaction was carried out in the absence of vinyl ether, affording a set of separable diastereomeric products. Plausible mechanisms for these transformations are discussed; a gold-containing benzopyrylium was regarded as the crucial intermediate by which a number of these new transformations took place.
Department of Chemistry, University of Louisville, 2320 South Brook Street, Louisville, KY 40208, USA.
Deepika
D
Malhotra
Le-Ping
LP
Liu
Mark S
MS
Mashuta
G B
GB
Hammond
D001547:Benzaldehydes / Q000138:chemical synthesis / Q000737:chemistry*; D001578:Benzopyrans / Q000138:chemical synthesis* / Q000737:chemistry; D001643:Bridged Bicyclo Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D002384:Catalysis; D003500:Cyclization; D006046:Gold / Q000737:chemistry*; D009281:Naphthalenes / Q000138:chemical synthesis* / Q000737:chemistry; D009795:Octanes / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism; D014753:Vinyl Compounds / Q000138:chemical synthesis / Q000737:chemistry*
D001547:Benzaldehydes; D001578:Benzopyrans; D001643:Bridged Bicyclo Compounds; D009281:Naphthalenes; D009795:Octanes; D014753:Vinyl Compounds; C100195:vinyl ether; D006046:Gold; C032175:benzaldehyde