O[C:2]1[CH:7]=[CH:6][N:5]2[C:8]([C:11]3[CH:16]=[CH:15][CH:14]=[CH:13][CH:12]=3)=[CH:9][N:10]=[C:4]2[C:3]=1[C:17]#[N:18].O(Cl)[Cl:20].[P+5].C([O-])(O)=O.[Na+].P(Cl)(Cl)(Cl)=O>CCOCC.CCOC(C)=O>[Cl:20][C:2]1[CH:7]=[CH:6][N:5]2[C:8]([C:11]3[CH:16]=[CH:15][CH:14]=[CH:13][CH:12]=3)=[CH:9][N:10]=[C:4]2[C:3]=1[C:17]#[N:18]
A mixture of compound D5 (2.3 g, 9.77 mmol) and phosphorus(V) oxychloride (50 ml) was heated at 120° C. for 5 h. After cooling to room temperature the solvents were evaporated in vacuo. The residue thus obtained was carefully poured into a mixture of crushed ice and NaHCO3 (aqueous sat. solution). Then EtOAc was added and the mixture was stirred for 2 h. until complete hydrolysis of the remaining phosphorus oxychloride had occurred. The organic layer was then separated, washed with brine, dried (Na2SO4) and the solvent evaporated in vacuo to give a residue that forms a precipitate upon the addition of Et2O. The solid was filtered off and dried in vacuo to yield compound D6 (0.82 g, 33%) as yellow solid.
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