Oxetanes, reactions with phosphorus

A. 3-Methyl-3-(toluenesulfonyloxymethyl)oxetane [Oxetane tosylate, ( )]. A dry, 1-L, round-bottomed flask is charged with a-toluenesulfonyl chloride (57.20 g, 0.30 mol) (Note 1) to which pyridine (250 mL) (Note 2) is added while stirring is carried out under nitrogen with a magnetic stir bar (Note 3). The reaction flask is placed inside a container to which an ice/water mixture may be added in the event that the reaction becomes too exothermic. 3-Methyl-3-oxetanemethanol (20.4 g, 0.2 mol) (Note 4) is added slowly and stirred for 1.5 hr. The mixture is slowly added to a vigorously (Note 3) stirred mixture of deionized water (700 mL) and crushed ice (700 g) in a 2-L Erlenmeyer flask and allowed to stir for ein additional 0.5 hr. The white precipitate is collected on Whatman filter paper 1 and washed with cold water (HjO, Note 5). The product is dried under high vacuum and/or phosphorus pentoxide (P2O5) to obtain the white powder of oxetane tosylate 1 (39.8-44.60 g, 78-87%) (Note 6). 

The report on the synthesis of the phosphonate isostere of AZT 5 -phosphate by a BF3-Et20-catalyzed nucleophilic addition of diethyl methanephosphonate to an oxetane prompted us to apply the same reaction conditions to the opening of epoxides. Indeed, when the anion of the same phosphonate was generated with BuLi in THF, followed by the sequential addition of epoxide 10a or 10b and BF3-Et20 at -78°, the corresponding P-hydroxyphosphonates 20 (a and c) were obtained in quantitative yield.26 Extension of this reaction to a phosphorus nucleophile proved to be equally effective. Thus, when diethyl phosphite was condensed with the same epoxides under identical reaction conditions, the corresponding P-hydroxyphosphonates 20 (b and d) were isolated in... 

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