| Abstract
| - A series of tungsten-η1-alkynols tethered with a dimethylacetal, methyl ketone, or trimethoxymethanegroup are prepared. Treatment of these functionalized tungsten-alkynols with BF3·Et2O leads tointramolecular cycloalkenation, producing bicyclic tungsten-oxacarbeniums in high yields. Airoxidation of these oxacarbenium salts produces unsaturated bicyclic lactones in good yields. Thelactone products include δ- and ε-lactones fused with five-, six- and seven-membered carbocyclicrings. The preceding bicyclic tungsten-η1-oxacarbeniums are highly reactive toward organocuprates,Grignard reagents, and diazomethane, leading to demetalation to give various derivatives of bicycliclactones. A short synthesis of (±)-mitsugashiwalactone is developed based on this method.
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