N,TV-Dimethylformamide

A mixture of l-deoxy-3,4-0-isopropylidene-l-phenylthio-L-erythrulose (1 6.0 g, 24 mmol) [57] and N,tV-dimethylformamide dimethyl acetal (4.25 g, 36 mmol) was stirred for 2 h at 70°C. The liberated methanol and the excess of the reagent were evaporated under reduced pressure and the dark oily residue was purified on a silica gel column with ethyl acetate as eluent to yield 2 (6.21 g, 85%) as a yellow solid mp 93°C (from diisopropyl ether). 

Other solvents may also be used with similar effects. Isopropyl alcohol has been used for fractionating a polyglucose.72 Examination of the fractions revealed that fractionation according to viscosity and immunological reactivity had occurred.240 The excellent solvent properties of methyl sulfoxide,241 tetramethylene sulfone, pyridine, N, TV-dimethylformamide, and formamide may also prove useful. 

Benzoylamino-6 -pyrido[l,2-a]pyrimidin-6-one 224 was prepared starting from 2-methylpyrimidine and N.TV-dimethylformamide dimethyl-acetate in boiling dimethylformamide (91BSB533). Then the resulting 2-[( )-2-(N,N-dimethylamino)ethenyl)]pyrimidine was reacted with 2-phenyl-5(4//)-oxazolone in refluxing acetic acid to give 6-oxopyrido-[l,2-a]pyrimidine 224 in 33% yield. 

Reaction of the diol with p-toluenesulfonyl chloride in pyridine, however, produced the ditosylate in nearly quantitative yield. SN2 displacements by chloride on neopentyl tosylate, which bears certain structural similarities to the ditosylate precursor of CAMPHOS, have been shown to give good yields of neopentyl chloride. However, when l,2,2-trimethyl-l,3-bis(hydroxymethyl)-cyclopentane ditosylate was allowed to react with sodium chloride in hexa-methylphosphoramide, in an attempt to form the dichloride, only N, A -dimethyl-p-toluenesulfonamide was isolated. Reaction of the ditosylate with lithium chloride in ethoxyethanol was exothermic and HC1 was evolved but the dichloride was not isolated. The isolated product contained at least one oleflnic bond. Similarly, in N, TV-dimethylformamide, lithium chloride and the ditosylate gave a product that decomposed on distillation. Faced with such repeated failures, a dihalide route to CAMPHOS was abandoned in favor of a more direct approach reaction of the ditosylate with diphenylphosphide anion. 

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