[H-].[Na+].[N:3]1[C:16]2[NH:15][C:14]3[C:9](=[CH:10][CH:11]=[CH:12][CH:13]=3)[S:8][C:7]=2[N:6]=[CH:5][CH:4]=1.C[C:18]#[C:19][C:20]([O-:22])=[O:21].[CH2:23](COC)OC>>[C:20]([CH:19]=[CH:18][N:15]1[C:16]2[N:3]=[CH:4][CH:5]=[N:6][C:7]=2[S:8][C:9]2[C:14]1=[CH:13][CH:12]=[CH:11][CH:10]=2)([O:22][CH3:23])=[O:21]To a suspension of sodium hydride (0.1 g, 4.2 mmoles) in dimethoxyethane (10 ml) was added 1,4-diazaphenothiazine (200 mg, 1 mmole). After stirring for 30 minutes a deep red solution of the anion was obtained and this was treated with methylpropiolate (85 μl, 1.0 mmole). Stirring was maintained for 30 minutes. The mixture was evaporated to dryness and the residue was purified by chromatography. Elution with 40% EtOAc/hexane gave the desired product as on orange solid, m.p. 165°-169°. NMR analysis showed the product to be a mixture of trans and cis isomers in a ratio of 4 to 1.
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