A solution of allyl (1S,5R,6S)-6-[1(R)-allyloxycarbonyloxy-ethyl]-2-hydroxymethyl-1-methyl-carbapen-2-em-3-carboxylate (365 mg, 1.0 mmol), triphenylphosphine (315 mg, 1.2 mmol), and 9,9-dioxo-6-(2-triethylsilanyloxy-ethyl)-10H-9-thia-10-aza-phenanthrene (429 mg, 1.1 mmol) in anhydrous tetrahydrofuran (7.3 mL) is cooled in an ice-bath and stirred under a nitrogen atmosphere while diisopropyl azodicarboxylate (0.24 mL, 1.2 mmol) is added dropwise over a few minutes. The resulting solution is stirred in the cold for 30 minutes, then diluted with chloroform, washed with 5% aqueous sodium bicarbonate and brine, dried over sodium sulfate, filtered and evaporated under vacuum. The residue is purified by silica gel flash chromatography , eluting with hexane-ethyl acetate, to afford allyl (1S,5R,6S)-6-[1(R)-allyloxycarbonyloxy-ethyl]-2-[9,9-dioxo-6-(2-triethylsilanyloxy-ethyl)-10H-9-thia-10-aza-phenanthren-10-ylmethyl)-1-methyl-carbapen-2-em-3-carboxylate.
