title: Efficient Synthesis of Bicyclic Lactones via Tungsten-Mediated Intramolecular Cycloalkenation.
abstract: A series of tungsten-eta(1)-alkynols tethered with a dimethylacetal, methyl ketone, or trimethoxymethane group are prepared. Treatment of these functionalized tungsten-alkynols with BF(3).Et(2)O leads to intramolecular cycloalkenation, producing bicyclic tungsten-oxacarbeniums in high yields. Air oxidation of these oxacarbenium salts produces unsaturated bicyclic lactones in good yields. The lactone products include delta- and epsilon-lactones fused with five-, six- and seven-membered carbocyclic rings. The preceding bicyclic tungsten-eta(1)-oxacarbeniums are highly reactive toward organocuprates, Grignard reagents, and diazomethane, leading to demetalation to give various derivatives of bicyclic lactones. A short synthesis of (+/-)-mitsugashiwalactone is developed based on this method.
authors.affiliation: Department of Chemistry, National Tsing-Hua University, Hsinchu, 30043 Taiwan, R.O.C.
authors.forename: Kwei-Wen
authors.initials: KW
authors.lastname: Liang
authors.forename: Malapaka
authors.initials: M
authors.lastname: Chandrasekharam
authors.forename: Chien-Le
authors.initials: CL
authors.lastname: Li
authors.forename: Rai-Shung
authors.initials: RS
authors.lastname: Liu