3,3-Dimethylglutaric anhydride → 2H-Pyran-2-one, tetrahydro-4,4-dimethyl-

A suspension of 5.8 g (0.15 mole) of sodium borohydride in 30 ml of dry tetrahydrofuran was stirred and cooled in an ice bath under nitrogen while 21.32 g (0.15 mole) of 3,3-dimethyl glutaric anhydride in 120 ml of dry tetrahydrofuran was added in 5 minutes. The ice bath was then removed and stirring was continued for 2 hours. Hydrochloric acid (6N, 60 ml) was added cautiously and the mixture was then concentrated in vacuo. Water (300 ml) was added and the mixture was extracted with ethyl ether. The ethyl ether extract was dried over anhydrous Na2SO4, concentrated in vacuo and distilled (60°, 1 mm Hg) giving 13.1 g (68.2%) of 3,3-dimethyl valerolactone with consistent 1H-NMR spectral data. This lactone (5 g, 39.04 mmole) and triphenyl phosphine hydrobromide (13.56 g, 39.04 mmole) were heated neat under nitrogen at 175° (oil bath temperature) for 3.5 hours. The reaction mixture was cooled to room temperature, diluted with 100 ml of water-ethyl acetate (1:1) and the phases were separated. The aqueous phase was washed again with ethyl acetate, treated with charcoal, filtered and lyophilized to yield 12 g (65.2%) of 4-carboxy-3,3-dimethylbutyltriphenylphosphonium bromide with consistent 1H-NMR spectral data. This was dried (65°, 0.3 mm Hg, 18 hours) prior to use.