[CH2:1]([CH:4]([CH2:8][C:9]#[CH:10])C(O)=O)[C:2]#[CH:3].C([N:13]([CH2:16]C)CC)C.C1(P(N=[N+]=[N-])(C2C=CC=CC=2)=[O:25])C=CC=CC=1.[C:35]([OH:39])([CH3:38])([CH3:37])[CH3:36]>C1(C)C=CC=CC=1>[C:35]([O:39][C:16]([NH:13][CH:4]([CH2:1][C:2]#[CH:3])[CH2:8][C:9]#[CH:10])=[O:25])([CH3:38])([CH3:37])[CH3:36]To a solution of 2-(2-propynyl)-4-pentynoic acid 42 (25.0 g, 0.184 mol) in toluene (200 ml) was added triethylamine (19.5 g, 0.193 mol) with cooling. Diphenylphosphoryl azide (50.5 g, 0.184 mol) was added, and the mixture was stirred at room temperature for 15 minutes. The mixture was heated on the steam bath until the reaction became exothermic. When the reaction subsided, the heating was continued for an additional 10 minutes during which time the evolution of gas ceased. Dry t-butanol (150 ml) was added, and the mixture was heated at reflux on the steam bath for 24 hours. The solvent was removed under vacuum, and the residue was diltued with water and extracted twice with diethylether. The combined aqueous extracts were washed with water (2×), 10% sodium carbonate solution, and brine. The solution was dried (MgSO4), and the solvent was removed under vacuum to leave crude 43 as a red-brown solid (35.35 g). A sample (3.2 g) was purified via flash chromatography (230-400 mesh silica gel, 10% ethyl acetate in hexane) to give a colorless solid (2.69 g). Crystallization from hexane gave the title compound (43) as colorless crystals (m.p. 64-67° C.).
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