2 4 2 7 1h m 4 25 2h q j 7hz 5 0 5 4 1h m 5 5 5 8 2h m 5 95 1h s or film v max 2960 1750 1670 1630 1470 1450 1370 1260 cm 1 ms m e 280 224 190 175 134 108 a mixture of 3 oxo u03b1 ionol 271g 1 3 mol diethyl carbonate 1 5l and dibutyl tin oxide 16g was heated at 105 115 u00b0 c for 40 hours during the reaction ethanol was removed by distillation distillation of the crude product provided 173 2g of material which glc analysis indicated contained 51 5 of 4 3 hydroxyl1 butenyl 3 5 5 trimethyl 2 cyclohexen 1 one ethyl carbonate further purification by chromatography provided 72 56g of carbonate 4 glc purity 85 a solution of ethyl chloroformate 1 74g 0 016 mol in dichloromethane 10ml was added dropwise over a 1 hour period to a cold 5 u00b0 c solution of 4 oxo u03b2 ionol 3 33g 0 016 mol which may be prepared as described by r kaiser and d lamparsky helv chim acta 1978 61 2328 2335 pyridine 1 28g 0 016 mol and dichloromethane 30ml after stirring the mixture at 5 10 u00b0 c for 2 hours it was added to ice water 20ml the organic layer was washed with 5 phosphoric acid solution until neutral and dried over sodium sulfate the solvent was removed and the residue chromatographed kugelrohr.