2.3- Dihydrofuran, thermal decomposition

Thermal decomposition of y-lactone tosylhydrazone sodium salts are reported to yield cyclobu-tanones, which can be accounted for by rearrangement of an intermediate oxycarbene. In this manner, the sodium salts of dihydrofuran-2(37/)-one tosylhydrazones 1 were decomposed as a loose powder, at 310 C in a bulb-to-bulb distillation apparatus at an initial pressure of 0.1 Torr, to give the corresponding cyclobutanones 2 in addition to enol ethers, cyclopropanes and open-chain alkenes. Condensable products (74-76%) were collected at — 78 °C, weighed and the ratio of components was determined from their relative GC peak areas.63... 

The major reaction in the thermal decomposition of 2,3-dihydrofuran (9) is a unimolecular isomerization to cyclopropanecarboxaldehyde (89JPC-1139). In an analogous [1,3] sigmatropic reaction, the isomerization of 2-methyl-4,5-dihydrofuran (10) leads to acetylcyclopropane, which can rearrange to 3-penten-2-one (94JPC2341). The latter product may also be formed directly from 10. 

The thermal stability of this polymer has been studied, and by heating from ambient to 500° C the polymer generates butadiene, tetrahydrofuran, dihydrofuran, water, the cyclic ester of phenylphosphonic acid and 1,4-butanediol, phenylphosphonic acid, and butanediol [1]. The same report evaluates thermal decomposition of this polymer end capped with phenylisocyanate. In addition to the same compounds as for the main polymer, CO2 and aniline were detected from the polymer decomposition. 

Triazolines from the cyclic enol ethers, dihydrofuran and dihydropyran, decompose at 100-130° into anils and nitrogen. Thus p-bromophenyl azide reacts with dihydropyran (69) to give triazoline 70 which decomposes thermally into the aryl-inline of 5-valerolactone (71). Photochemical decomposition of 70, on the contrary, yields 7-p-bromophenyl-7-aza-2-oxabi-cyclo[4.1.Q]heptane (72) in 67% yield. Scheiner has shown that aziridine 72 is stable at the decomposition temperature of 70, proving that it is not an intermediate in the thermal conversion of 70 to 71. 51... 

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