Routes to simple 3-substituted oxetanes
This thesis describes syntheses and attempted syntheses of certain 3-substituted oxetanes. Simple oxetanes bearing reactive substituents in the 3-position are required since the polymerisation of these compounds is anticipated to lead to polymers of potential use as energetic binders in rocket propellant systems. Oxetanes of particular interest are 3-hydroxyoxetane, 3,3-bis(hydroxymethyl)oxetane, and 3-(hydroxymethypoxetane. 3-Hydroxyoxetane was prepared in three steps from epibromohydrin (I). Firstly, Lewis acid-catalysed ring opening of the epoxide in the presence of acetic acid gave the bromohydrin II. This was heated with ethyl vinyl ether and p-toluenesulphonic acid, and cyclisation of the resulting ether III with strong base afforded the oxetane IV. Deprotection gave 3-hydroxyoxetane (V). 3-Hydroxyoxetane (V) underwent reaction with dinitrogen pentaoxide, and the resulting nitrate ester VI was polymerised to give poly-3-nitratooxetane 3,3-Bis(hydroxymethyl)oxetane (IX) was prepared from pentaerythritol (VIII) via pyrolysis of the carbonate ester X, and by monobromination followed by intramolecular Williamson reaction of the resulting bromohydrin XI. Attempts have been made to synthesise 3-(hydroxyMethypoxetane (XII) by two main routes. The first involved cyclisation of either 2-(hydroxymethyl)propane-1,3-diol (XIII) or a protected derivative XIV to give either the oxetane XII itself or the corresponding derivative XV. 2-(Hydroxymethyl)propane-1,3-diol (XHI) was itself prepared by deamination of 2-amino-2-(hydroxymethyl)propane-1,3-diol (XVI) using hydroxylamine-0- sulphonic acid in base, but it could not be cyclised directly. 2,2-Dimethy1-5-(hydroxymethyl)-5-nitro-1,3-dioxane (XVIII) was formed by the reaction of 2-(hydroxymethyl)-2-nitropropane-1,3-diol (XVH) with 2-methoxypropene. The dioxane XVIII was further protected by conversion to 2,2-dimethy1-5- (methanesulphonyloxymethyl)-5-nitro-1,3-dioxane (XIX). Hydro-denitration of the nitro-compound XIX using tri-n-butyltin hydride, yielded 2,2-dimethy1-5- (methanesulphonyloxymethyl)-1,3-dioxane (XX), which was hydrolysed to the corresponding diol XXI. Treatment of this methanesulphonyl ester XXI with strong base afforded 3-(hydroxy/methypoxetane (XV). An attempt to form 2(t-butyldimethylsilyloxymethyppropane-1,3-diol (XXII) via a five-stage process from allyl t-butyldimethylsilyl ether (xxim) was unsuccessful. Cyclo-addition of the allyl ether XXIII with dichloroketene gave 3-(tbutyldimethylsilyloxymethyl)- 2,2-dichlorocyclobutanone (XXIV) which was dehalogenated to give 3-(t-butyldimethylsilyloxymethyl)cyclobutanone (XXV). This was converted to diethyl acetal XXVI, but the acetal failed to undergo Baeyer-Villiger oxidation to 5-(t-butyldimethylsilyloxymethyl)-2-oxo-1,3-dioxane (XXVII). A second route to 3-(hydroxymethyl)oxetane (MI) involved the formation and attempted cyclisation of the glycidyl ether XXVIII to give oxetane XXIX. The epoxide XXVIII was prepared from ethyl bromoacetate and glycidol, but no cyclisation could be effected.