Oxetenes

MO calculations, 7, 364 Oxetene, 2-isopropylidene-polysubstituted rearrangement, 7, 377 Oxetene, tetramethyl-structure, 7, 366 Oxetenes, 7, 363-402 decomposition, 7, 375 metabolism, 1, 243 molecular dimensions, 7, 366 thermal stability, 7, 370 Oxetenyl anions aromaticity, 7, 371 Oxetenyl cations aromaticity, 7, 371 Oxichlororaphine occurrence, 3, 196 Oxichromic developers in colour photography, 1, 378-379 Oxidation... 

Geomycin (Otsuka) Oxeten (Mochida) Terramycin (Taito Pfizer) Terra-Cortril (Pfizer) Terramycin (Pfizer) Urobiotic-250 (Pfizer)... 

The [2h-2] cycloaddition could occur thermally in the pseudoexcitation band. In fact, an alkyne with electron-donating group, ethoxyacetylene, and electron accepting carbonyl compound, perfluoroacetone, form the oxetene at low temperature (-78 °C) without light irradiation (pseudoexcitation band in Scheme 6) [26, 27],... 

The above-postulated overall mechanism considers two alternative pathways depending on the nature of the acetylene derivative. Region A outlines a proposal in which the formation of the a-complex intermediate is supported by the fact that the treatment of aliphatic terminal acetylenes with FeCl3 led to 2-chloro-l-alkenes or methyl ketones (Scheme 12). The catalytic cycle outlined in region B invoked the formation of the oxetene. Any attempt to control the final balance of the obtained... 

Irradiation of benzaldehyde in the presence of S-decyne results in the formation of the above a,/3-unsaturated ketone, presumably from decomposition of an intermediate oxetene which may be formed in a vibrationally excited (hot) ground state.<106)... 

Similarly to aldehydes, esters add to acetylenes to produce unstable oxetenes which decompose to j8-alkoxy-a-benzoylstyrene derivatives when diphenylacetylene is used.<108) For example,... 

The first reliable synthesis of an oxetene was that of the 2-ethoxy-4,4-di(trifluoromethyl) derivative in 1965, by reacting di(trifluoromethyl) ketone with ethoxyethyne at -78 °C (Scheme 8.11). At room temperature the product undergoes ring fission to ethyl 3,3-bis(trifluo-romethyl)propenoate. 

This is also the case with the oxetenes formed by photocycloaddition to acetylenes. Irradiation of benzaldehyde in the presence of 5-decyne... 

I Compound obtained as result of decomposition of oxetane (or oxetene). 

Ab initio MO calculations with the same two types of basis sets have been performed for oxetene (1) and for the oxetenyl anion (2) and cation (3) with excellent agreement observed between the STO-3G and 4-31G results. Complete molecular dimensions were derived for all three species (80TL1807). 

Phenyl- and vinyl-substituted oxetanes are more labile and tend to decompose at 250-300 °C. 2-Oxetanones are very sensitive to thermolysis, often decomposing with loss of carbon dioxide at temperatures of about 100 °C. Oxetenes are thermally unstable at room temperature. 

It was found that anion (2) has about 80 kJ mol-1 more stabilization than the hypothetical model (19a). This shows that there is a substantial amount of stabilizing resonance energy, which is in accord with its having a cyclic 67r-electron system. The stabilization is not great enough, however, for oxetene to be expected to show appreciable acidic properties. Calculations show oxetene to be less acidic than propene. 

---