Ring Transformation into other Three-Membered Heterocycles

Ring Transformation into other Three-Membered Heterocycles 

A single-step synthesis of aziridines has been described by nucleophilic attack of an amidophosphate ester anion on the least-substituted carbon atom of oxiranes (Eq. 181).  

Anew synthetic method involves reaction with an A -substituted iminophosphorane, which is accompanied by oxygen-nitrogen heteroatom exchange (Eq. 182).  

With phenoxymethyloxirane the reaction takes place through a five-membered cyclic intermediate (Eq. 183).  

Oxygen-sulfur heteroatom exchange has been achieved with 3-methyl-benzene thiazole-2-thione in the presence of trifluoroacetic acid and with l-phenyl-5-mercaptotetrazole. Thiirane can be prepared from oxirane on a support impregnated with alkali metal salts, by decomposition of the dithiocarbon-ate formed with carbon disulfide. A macrocyclic ether, perhydrobenzo-18-crown-6, plays a role in the nucleophilic reaction of oxirane with KCNS, which leads to thiirane in good yield.  

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A. Ring Transformation into other Three-Membered Heterocycles... 

The first example in Scheme 10.1 shows that vinylphosphine kinetically first gives the three-membered heterocycle (75%), which upon heating transforms into the thermodynamic product, the four-membered heterocyclic complex. From the other examples we see that, ifthe possibility exists, the preferred route is formation ofa fivemembered ring [18]. 

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