Oxetan ions, decomposition

Transfer to polymer (Sect. 5.3) has been described by Aleksiuk a.o. in polymerization of 3-chloromethyl-3-methyloxetane initiated with aluminum allQ ls. High molecular weight polymers (M = 6 to 8 10 ) with narrow molecular weight distribution (Mw/M = 1.29) were formed from very beginning of reaction and were independent of conversion. These data suggest slow initiation, fast propaption and unimolecular decomposition process. Authors propose the termination on the own polymer backbone and formation of nonreactive branched oxonium ion. Similar mechanism described earlier for 3,3-bis(chloromethyl)oxetane is discussed in Sect. 3.2.11. 

The reason that esters frequently give better yields of oxetane is not known, but it seems likely that reaction of hydroxide ion would u> primarily on the carbonyl carbon atom, to form an Intermediate of i fa> usual type- This might reasonably decompose either (a) with con carted attack on the halogeii-subetituted carbon atom, or (b) inii. -i 3-halogenoalkoxide ion which is thermally activated by tlw he i.l decomposition of the intermediate, thus fadlitating ring cloeure. 

Spiro-oxetans (58) are formed as minor products in the decomposition of aryldiazomethanes in the presence of p-chloranil. The bromonium ion that is derived from (59) suffers intramolecular attack by the hydroxy-group by a 4-exo-tet. rather than a 5-endo-tet. pathway, to give the oxetan (60). This undergoes stereospecific dehydration to (61). ... 

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