Oxetane reaction with carbenes

The reaction of ethoxycarbonylcarbene with phenyloxetane gives an excellent yield of 2-ethoxycarbonyl-3-phenyltetrahydrofuran, showing insertion between the oxygen atom and C-2 had occurred. The first step is believed to be attack of the carbene on the oxygen atom (66T3393). In contrast, ethoxycarbonylnitrene inserts into an a-CH bond of oxetane, as with other cyclic ethers (76BCJ2572). 

The reaction of oxetane with carbenes follows two major pathways carbonhydrogen insertion or the formation of an oxygen ylide by reaction of the carbene and the oxetane oxygen. The oxygen ylide can produce a tetrahydrofuran by a Wittig rearrangement or generate an allyl ether by an intermolecular -elimination process (Scheme 61). 

The intermolecular reaction of a carbene with an oxetane results in the formation of an oxonium ylide that is further stabilized via either opening... 

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