Ethyl Acetate → (2S,5S)-1-tert-butyl 4-methyl 2-((tert-butyldimethylsilyloxy)methyl)-5-hydroxy-5,6-dihydropyridine-1,4(2H)-dicarboxylate

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A stirred solution of methyl 4-(tert-butoxycarbonyl((S)-1-(tert-butyldimethylsilyloxy)but-3-en-2-yl)amino)-3-hydroxy-2-methylenebutanoate (Intermediate 100, 16 g, 37 mmol) in toluene (about 300 mL), at ambient temperature in a heat-dried flask, was thoroughly degassed with argon and placed under a nitrogen atmosphere. To this was added Hoveyda-Grubbs Catalyst 2nd Generation (460 mg, 0.74 mmol). Analysis of the mixture 3.5 hours later by LCMS and TLC (15% ethyl acetate in hexanes) indicated very high conversion of starting material to two major products. The reaction mixture was concentrated in vacuo in the presence of enough silica gel to give a free-flowing powder upon reaching dryness. Normal-phase chromatography (0-100% ethyl acetate in hexanes, 330-g column, 45 minutes) was used to isolate the two compounds; the diastereomer shown above (6.4 g, 43%, dark oil) eluted first.

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