Oxetanes, pyrolysis

Oxetane, 3,3,4,4-tetramethyl-2,2-diphenyl-pyrolysis, 7, 372-373 Oxetane, vinyl-thermal stability, 7, 370 Oxetane-3-carboxylic acid, 3-hydroxy-2,2,4,4-tetramethyl-synthesis, 7, 394... 

Oxetan-2-one (j3-propanolactoiic) unci also oxetani-3-one are known, although most interest lies in the former compound. It is a carcinogen, possibly because it can alkylate guanidine, one of the constituent bases of nucleic acids. On standing, oxetan-2-one slowly polymerizes, and on pyrolysis it forms propenoic acid (Scheme 8.13). Alkaline hydrolysis gives a salt of 3-hydroxypropanoic acid. 

Photolysis of oxetane, 2,2-dimethyloxetane and 2-phenyloxetane has been found to occur slowly with mercury arc irradiation. The products are similar to those observed from pyrolysis of these compounds. Oxo-substituted oxetanes are probably much more susceptible to photolysis. Irradiation of oxo-oxetane (28) at 350 nm isomerized it to a furan (29) and a dioxalene (30), each of which can be explained by cleavage of the oxetane ring to a 1,4-biradical (69CC572). 

The mechanism of decarboxylation of /3-lactones has attracted much attention. The gas-phase decomposition of 2-oxetanone is a unimolecular first-order process. It has a considerably lower energy of activation than the pyrolysis of oxetane and a much higher entropy of activation, indicating a loose activated complex (69JA7743). The ease of the reaction is greatly affected by the electronic effect of substituents at position-4, but not at position-3. The Hammett treatment of a series of rrans-4-aryl-3-methyl-2-oxetanones gave a good correlation with [Pg.374]

There are other reactions which have been found to yield oxetanes but have not been developed as synthetic methods. The thermolysis and photolysis of y-methyl-y-peroxy-valerolactone gives 2,2-dimethyloxetane, presumably by way of a diradical intermediate (equation 87). This is the same type of intermediate involved in pyrolysis of the oxetane at a much higher temperature (71CC1299). Somewhat related are photochemical syntheses... 

In the present review the ring systems containing one heteroatom are considered first, except for P-lactams which are given a special section at the end. Interest in azetidines continues to be stimulated by the discovery of the potentially useful trinitro derivative. The requirements for the stereoselective synthesis of substituted oxetane are being explored and derivatives of aluminium are useful in the stereoselective routes to oxetanones. The preparation and subsequent pyrolysis of oxetanones is suggested as an alternative to the Wittig route to olefins. Stereoselective routes to thietanes and thietane 1 -oxides are mentioned. 

This eompouod (XCVI) was prepared by Applequiet and Roberts hy the pyrolysis at SflO" of 2>3,h,e diben2iOflpiTobicyolo[2.2.2]oetaQe-7,3 -oxetane (XCV). The compound was a liquid, b.p. 70 , with an... 

The cage compound (301) is formed efficiently on irradiation of the adduct (302).Irradiation of the ene dione (303) affords the cage compound (304) by a (6 + 2)-cycloaddition. The Diels-Alder adducts (305) are photochemically reactive. Irradiation of (305) affords either the cage compounds (306) by a (2+2)-cycloaddition reaction, a process favoured by the adducts (305 a,b), or the oxetanes (307). The structures (306, 307) were verified by 2L ray diffraction studies The quinone adduct (308) also undergoes photochemical cyclization to afford the cage diketone (309). This material was subjected to flash vacuum pyrolysis to yield the diketone (310) important in the synthesis of perhydroindacenes. ... 

At first glance it would seem that the formation of isomer pairs provides conclusive evidence of naphth[l,8-Z)c]oxete intermediate (27) involvement. However, taking into consideration the drastic pyrolysis conditions (680 °C) and the predicted instability of the naphth[l,8-Z)c]oxete (23) structure, it is more likely that not a four-membered oxetane heterocycle, but a pair of interconverting biradical intermediates A and B takes part in the reaction where the formation of the new C -O covalent bond occurs simultaneously with the rupture of the existing C -O bond (A- — B). 

The most versatile method involves rearrangement of an acylated hydroxymethyloxetane catalyzed by boron trifluoride etherate (13. 17). The triols are readily converted to the required hydroxymethyl oxetanes via pyrolysis of the carbonate esters (18) and then to the acylated hydroxymethyloxetanes with acid chlorides. 

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