Lithium thioethoxide was prepared by the dropwise addition of n-butyllithium (4 ml. of 1.53 molar solution in hexane) to a stirred solution of ethyl mercaptan (0.5 ml.) in dry N,N'-dimethylpropylene urea (DMPU) (9 ml.), under a nitrogen atmosphere. A solution of methyl 4-(6-hexanamido-2,3-dihydrobenz-1,4-oxazin-4-ylmethyl)-3-methoxybenzoate (prepared as described in Example 26) (0.35 g.) in DMPU (3 ml.) was added, the mixture stirred at ambient temperature for 15 minutes, then heated to, and maintained at, 130° C. for 4 hours. The cooled mixture was diluted with water, acidified with acetic acid, extracted with ethyl acetate, the extracts washed with water, dried (MgSO4) and evaporated. The product was purified by flash chromatography on silica gel, eluting with 80:20:2 v/v/v toluene: ethyl acetate: acetic acid, giving a white solid which was washed with hexane and dried, to give the title compound (0.114 g., 36%) as a white solid, m.p. 183°-184° C.
