A mixture of dimethyl (R,R)-2-allyl-1,3,2-dixoaborolane-4,5-dicarboxylate (0.67M in toluene, 1.8 ml, 1.2 mmol) and 0.4 nm molecular sieves (50 mg) was stirred at 20° C. for 10 minutes and then cooled to −70° C., and then a solution of diphenylmethyl (4R, 6R, 7R)-3-formyl-7-phenylacetamidoceph-2-em-4-carboxylate (100 mg, 0.2 mmol) in tetrahydrofuran (0.5 ml) was added dropwise. After 2 h at −70° C. the mixture was warmed to 20° C. and water and ethyl acetate were added. The organic layer was dried (MgSO4) and evaporated and the residue purified by chromatography as in part a to give the title compound S-diastereomer, 45 mg (43%), and the R-diastereomer 8 mg (8%).
