Reactions of Oxetane

Anions of small heterocyclics are little known. They seem to be involved in some elimination reactions of oxetan-2-ones (80JA3620). Anions of large heterocycles often resemble their acyclic counterparts. However, anion formation can adjust the number of electrons in suitable systems so as to make a system conform to the Hiickel rule, and render it aromatic if flat geometry can be attained. Examples are found in Chapter 5.20. Anion formation in selected large heterocycles can also initiate transannular reactions (see also Section 5.02.7 below). 

Bis(3-nitrofurazanoxymethyl)oxetane 221 was synthesized in 52% yield by base-promoted ring closure of the corresponding 3-hydroxy-l-propyl triflate, 219, which is readily available from the diol and triflic anhydride. Oxetane 221 can also be prepared in 74% yield by treatment of the trifurazanyl ether 220 with DBU. Polymerization and copolymerization reactions of oxetane 220 have also been investigated (97MI7) (Scheme 148). 

Fig. 19 Polymerization reaction of oxetane and CO2 catalyzed by (salen)CrCl and two equivalents of n-Bu4NBr at 70°C (salen ligand contains a cyclohexylene backbone for the diimine and t-butyl substituents in the 3,5-positions of the phenolates). (a) Three-dimensional infrared traces of the closely overlapped VCO2 bonds of TMC and poly(TMC). (b) Reaction profile as a function of time, where only a select number of composite infrared bands were deconvoluted...

The acid-catalyzed reaction of oxetanes with t- butyl isocyanide gives 2-iminotetra-hydrofurans, boron trifluoride etherate being used as catalyst (equation 26). The authors proposed that the isocyanide reacts with the protonated oxetanes by an N2 mechanism (70S475). 

Enol alkylation of cyclohexanone by oxetane has been achieved by the reaction of oxetane with an enamine salt, bromomagnesium Af-cyclohexyliminocyclohexane, in THF. An 80%... 

The reaction of oxetanes with Grignard reagents and organolithium compounds is well known and has been useful, particularly with oxetane itself. A recent application involves use of the reaction of isopentylmagnesium bromide with oxetane as the first step of a synthesis of an insect pheromone (equation 43) (76CB3375). The Grignard reaction with 2-methyloxetane and 2-phenyloxetane is less satisfactory, due to the extensive formation of by-products. 

A few years later, Baba reported a more comprehensive description of the coupling reaction of oxetane and C02 catalyzed by organotin iodides and Lewis bases as catalysts [60]. It was shown in this instance, that the choice of Lewis base which coordinated to the organotin iodides affected the catalytic activity and selectivity, that is, poly(TMC) and/or trimethylene carbonate. Whilst complexes with Bu3P yielded polycarbonate, the combination of Bu3SnI with Bu3P=0 yielded TMC exclusively in good yields. A reaction mechanism, as proposed by Baba and coworkers, is illustrated in Scheme 8.5. 

Reports of anionic polymerization reactions of oxetane monomers are less common in the literature, than the generally applied cationic method. While unsubstituted oxetanes have been successfully converted to their corresponding... 

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 ring-opening reactions of oxetans by phosphorus trichloride have been further studied, and the effects of changing reagent ratios assessed the pathway to the esters (46) is outlined below. Chlorodi-isopropylphosphine (47)... 

Amongst the few reported reactions of oxetans is their non-stereospecific conversion into oxazines when treated with nitriles and the reaction of the (R)-lactone (44) with a Grignard reagent as the key step in a novel synthesis of (i ,/ )-phytol. ... 

Other reactions of oxetanes reported include the asymmetric ring expansion of 2-substituted oxetanes in an enantioselectively catalysed reaction with diazoacetic esters to give 2,3-disubstituted tetrahydrofiirans <01T262I>, and the Lewis acid promoted reactions of 2-methoxy-2-siloxyoxetane with allylsilane <00MI651 >. 

S3mthesis of polymers with well-defined structures by novel ring-opening reactions of oxetanes 06Y934. 

Fluorinated five- to seven-membered cyclic ethers have been stereoselectively synthesized from iodoalkyl substituted four- to six-membered cyclic ethers by fiuorinative ring-expansion reaction using difluo-roiodotoluene [31]. Scheme 3.10 shows a specific example of a fiuorinative ring-expansion reaction of oxetanes 24 leading to five-membered cyclic ethers 25 [31]. 

The reaction of epoxides with isocyanates is well known, but less well known is the reaction of oxetanes with isocyanates. However, the modified reaction conditions reported for epoxide... 

Darensbourg, D.J., Moncada, A.I., 2008. Mechanistic insight into the initiation step of the couphng reaction of oxetane or epoxides and CO2 catalyzed by (salen)CrX complexes. Inorganic Chemistry 47, 10000—10008. 

Darensbourg, D., Moncada, A.I., Choi, W., Reiebenspies, J.H., 2008. Mechanistic smdies of the copolymerization reaction of oxetane and carbon dioxide to provide aliphatic polycarbonates catalyzed by (Salen)CrX complexes. Journal of the American Chemical Society 130, 6523-6533. 

The reaction of oxirane and HI is significantly faster than the reaction of oxetane and HI. Draw the product of each reaction and suggest a reason for this difference in rate. 

Furthermore, the opening reactions of oxetane and tetrahydro-furan proceed nicely under these reaction conditions to give primarily the corresponding alcohols (eqs 18 and 19). 

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