Diethyl Ether → 3-Oxo-2-oxa-bicyclo[2.2.1]heptane-5-carboxylic acid tert-butyl ester

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Reaction Conditions

Reaction Steps

Compound 3b (13.9 g, 89 mmol) was dissolved in dichloromethane (200 ml) and then cooled to approximately −10° C. under nitrogen. Isobutylene was bubbled into the solution until the total volume had increased to approximately 250 ml which gave a “clowdy solution”. BF3×Et2O (5.6 ml, 44.5 mmol, 0.5 eq.) was added and the reaction mixture was kept at approximately −10° C. under nitrogen. After 10 min, a clear solution was obtained. The reaction was monitored by TLC (EtOAc-Toluene 3:2 acidified with a few drops of acetic acid and hexane-EtOAc 4:1, staining with basic permanganate solution). At 70 min only traces of compound 13 remained and aq. saturated NaHCO3 (200 ml) was added to the reaction mixture, which was then stirred vigorously for 10 min. The organic layer was washed with saturated NaHCO3 (3×200 ml) and brine (1×150 ml), then dried with sodium sulfite, filtered and concentrated into an oil containing small droplets. Upon addition of hexane to the residue the product crashed out. Addition of more hexane and heating to reflux gave a clear solution from which the product crystallized. The crystals were collected by filtration and washed with hexane (rt), then air-dried for 72 h which gave the title compound as colourless needles (12.45 g, 58.7 mmol, 66% from first harvest).

Provenance & Evidence