1.3.2- Oxazaphospholidine-2-thiones

Scheme 29 Synthesis of 2-chloro-1,3,2-oxazaphospholidine 2-thiones 101a,b...

A similar condensation of (+)-norephedrine (121) gave the corresponding 2-methyl-1,3,2 oxazaphospholidine-2-thiones 122a,b which were separated by rapid, medium pressure chromatography (Scheme 35) [67],... 

The initial C-0 bond cleavage (by attack of a/the bromide ion at the benzylic carbon, followed by recyclization of the intermediate 301 by selective alkylation at sulfur) was suggested to be responsible for a stereospecific rearrangement of 2-substituted-1,3,2 -oxazaphospholidine-2-thiones 299 derived from (-) pseudoephedrine into... 

Isopropyl-3,4-dime thyl-5-phenyl-1,3,2-oxazaphospholidine-2-thione, Z"6.8... 

The reaction of (-)-ephedrine (42) with thiophosphoryl chloride was reported to give 2-chloro-l,3,2-oxazaphospholidine 2-thione as the isomeric pair 101a,b, which could be separated by chromatography over silica gel [32] or recrystallization (Scheme 29) [55],... 

Treatment of (-)-ephedrine (42) with methylthiophosphonic dichloride afforded a mixture of the isomeric 2-methyl-l,3,2 oxazaphospholidine-2-thiones 120a,b, from which the pure isomers could be separated in approximately equal quantities by chromatography over silica (Scheme 34) [32],... 

Scheme 70 Stereospecific rearrangement of 2-substituted- l,3,2-oxazaphospholidine-2-thiones 299...

The Stereochemical Course of the Alkaline Hydrolysis of l,3,2-Oxazaphospholidine-2-thiones... 

The method chosen was that of Johnson and coworkers (ref. 66) which involves the use of a chiral oxazaphospholidine-2-thione as a chiral derivatising agent for Ip NMR analysis of... 

Cullis et al. (1987) have demonstrated that incubation of either diastereomer of the l,3,2-oxazaphospholidine-2-thione [33a] in anhydrous pyridine results in epimerization (ti = 12h at room temperature). This result was repeated with the thio derivatives [33b] (ti = 16h at 31°C) and in the case of [33a] with A, A -dimethylaminopyridine or 7V-methylimidazole in place of pyridine. In the latter experiments, it was postulated that the cyclic intermediates corresponding to [33c] are detected. Furthermore, incubation of either diastereomer of [33a] with tetrabutylammonium fluoride in the THF gives identical epimeric mixtures of product [33d]. 

As the NMR spectra of the phospholidine-thiones 2a and 2b do not permit to assign the configuration of the phosphorous chiral center,we have tried to grow crystals suitable for X-ray diffraction. We were successful only for a homologue of 2a with a shorter chain the crystal structure of the major (2-butanoxy-4-phenyl)1,3f2-oxazaphospholidine-2-thione (2a, R = Ci Hg), shows the relative S, R configurations on positions 2 and 4.° As the acid cleavage is expected to proceed with... 

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