Efficient Synthesis of Bicyclic Lactones via Tungsten-Mediated Intramolecular Cycloalkenation.
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.
Liang
Kwei-Wen
KW
Department of Chemistry, National Tsing-Hua University, Hsinchu, 30043 Taiwan, R.O.C.
Chandrasekharam
Malapaka
M
Li
Chien-Le
CL
Liu
Rai-Shung
RS