A mixture of 1.23 g of 1,2-dibenzyl 1-tert.butyl 4-methyl-1-(prop-2-en-1yl)-1,1,2(R)-pentanetricarboxylate, 3 ml of a 1% aqueous solution of osmium tetroxide, 2.44 g of sodium periodate, 15 ml of diethyl ether and 15 ml of water was stirred at room temperature for 1 hour. A further 3.25 g of sodium periodate were added and the mixture was stirred at room temperature for 24 hours. The ether layer was separated and the aqueous layer was extracted with diethyl ether. The combined ether layers were washed repeatedly with 5% aqueous ascorbic acid solution and saturated sodium chloride solution. After drying over magnesium sulfate, the solution was evaporated and the residue was purified by flash chromatography on silica gel using hexane/diethyl ether (8:1) for the elution. There was obtained 0.955 g of 1,2-dibenzyl 1-tert.butyl 1-(formylmethyl)-4-methyl-1,1,2(R)-pentanetricarboxylate in the form of a colorless oil; MS: 497 (M+H)+.
