[C:1]([N:8]1[C@H:12]([CH:13]=O)[C@@H:11]([CH3:15])[O:10][C:9]1([CH3:17])[CH3:16])([O:3][C:4]([CH3:7])([CH3:6])[CH3:5])=[O:2].[CH3:18]OP(C(=[N+]=[N-])C(=O)C)(=O)OC.C([O-])([O-])=O.[K+].[K+].[NH4+].[Cl-]>CO.CCOC(C)=O>[C:1]([N:8]1[C@H:12]([C:13]#[CH:18])[C@@H:11]([CH3:15])[O:10][C:9]1([CH3:17])[CH3:16])([O:3][C:4]([CH3:7])([CH3:6])[CH3:5])=[O:2]To a solution of (4S,5R)-N-Boc-2,2,5-trimethyl-oxazolidine-4-carbaldehyde (1.52 g, 5.43 mmol) (Example 102A above) and dimethyl(1-diazo-2-oxopropyl)phosphonate (1.57 g, 8.15 mmol) in dry MeOH (30 mL) was added K2CO3 at 0° C. The mixture was stirred at 0° C. for 30 min and room temperature for 20 h. After addition of saturated aqueous NH4Cl and EtOAc, the organic layer was separated and aqueous layer was extracted with EtOAc (3×). The ethyl acetate layers were combined and dried with MgSO4. The crude material was purified by flash column chromatography eluting with EtOAc/hexanes (1:6) to give (4R,5R)-N-Boc-2,2,5-Trimethyl-4-ethynyl-oxazolidine. (Yield 0.97 g, 65%).
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