From oxetanes

Exocyclic unsaturation can stabilize small ring heterocycles. In three-membered rings it is difficult to separate the contributions from increased angle strain and from electronic interactions between the unsaturation and the heteroatom. In four-membered rings such separation has been done 74PMH(6)199, p. 235). The CRSEs change from oxetane... 

A chiral version of the above-mentioned ring opening of oxetanes has been applied to chiral oxetanes. An example is shown in Scheme 90 starting from oxetane 303, which after DTBB-catalyzed (5%) lithiation in TFIF at 0°C gave the (/-functionalized organohthium intermediate 304, which by treatment with different electrophiles and final hydrolysis with water yielded the corresponding products 305 (Scheme 90) °. 

By using the aluminum porphyrin-Lewis acid system, we attempted the synthesis of a narrow MWD block copolymer from oxetane and methyl methacrylate (MMA). Methacrylic monomers can be polymerized radically and anioni-cally but not cationically, so a block copolymer of oxetane and methyl methacrylate has never been synthesized. As already reported, methacrylic monomers undergo accelerated living anionic polymerization with the (TPP)AlMe (1, X= Me)-3e system via a (porphinato)aluminum enolate as the growing species. 

Exocyclic unsaturation can stabilize small ring heterocycles. In three-membered rings it is difficult to separate the contributions from increased angle strain and from electronic interactions between the unsaturation and the heteroatom. In four-membered rings such separation has been done (74PMH(6)199, p. 235). The CRSEs change "from oxetane (106 kJ mol-1) by -11 kJ mol-1 to oxelan-2-one (95 kJ mol-1) (corrected for electronic effects) and 4-methyleneoxetan-2-one (95 kJ mol" ). In contrast, an increase of 10 kJ mol 1 over the value for cyclobutane (111 kJ mol-1) is observed on going to both methylenecyclobutane and l,3-bis(methylene)cyclobutane. 

Scheme 8.5 Reaction mechanism for production of poly(TMC) from oxetane/C02 using a BujSnl catalyst in the presence of Lewis bases.

A kinetic study of the ring-opening polymerization (ROP) of trimethylene carbonate similarly afforded AG at 383 K of 101.9 kj mol-1, a value which was very close in energy to that found for the production of poly(TMC) from oxetane and C02. Hence, based on these experimental findings, the formation of polycarbonate from the oxetane and C02 coupling reaction was shown to occur via two different or concurrent pathways-that is, the intermediacy of TMC formation, and the subsequent polymerization and/or direct enchainment of oxetane and C02 (Figure 8.16). The presence of small amounts of ether linkages in the copolymer also supported this conclusion. 

The molecular weight values of poly(TMC) obtained from oxetane and C02 in the presence of a (salen)CrCl/n-Bu4NN3 catalyst system were generally lower than the theoretical values (Mn = 11050 Mn (theoretical) = 85 000). This situation was most likely due to a chain transfer mechanism arising from the presence of trace amounts of water in the system. However, when the catalytic runs were carried out under rigorously anhydrous conditions, the molecular weights more closely tracked the predicted values. 

In all cases, the cyclic amino substituent in the major diastereoisomer is oriented cis to the aryl moiety of the participating aroyl group whereas the nonparticipating aroyl group is cis to the nitrile function. Whereas 2-naphthyl-substituted diones from oxetanes, 1,1 -naphthyl- and 1-(1-naphthyl)-2-phenyl ethanedione are unreactive. The latter effect probably reflects the nn nature of the lowest excited triplet state of these diones. 

Lo and Fu have developed a Cu(ii) catalyst based on chiral bidentate N,N-ligands that effects an enantioselective ring expansion of oxonium ylides derived from oxetanes and a-diazoesters of type 53 (Equation 98) <2001T2621>. 

Irradiation by a mercury arc cauecs oxetaiies to decompose pliotochemlcally i From oxetane were formed ethylene and formal-... 

Ethylene and formaldehyde are the main products from oxetane (91). Preliminary quantum yield values of some products from p-dioxane (186) and the tetrahydrofurans (188) are presented in Tables 14 and 15. In the case of p-dioxane one is led to propose... 

We have also been engaged in the development of synthetic chemistry of building blocks derived from oxetan-3-one (Scheme 13.6). In this regard, oxetan-3-one reacts with commercially available stabilized ylids to give unsaturated ester 8 and aldehyde 9 at remarkably rapid rates as well as 89% and 81% yield, respectively. This was surprising given the strain of the olefin produced and the problems that had been previously noted with 3-methylene oxetane, as well as the fact that... 

Energy transfer from excited species created by chemiluminescent reactions within polymers has been studied recently,149 151 in extension of previous work.180 The species formed in the more recent work are the acetone singlet and triplet states from oxetan thermal dissociation, and possible processes occurring with... 

Without additional reagents Ethylene derivs. from oxetans... 

Glycol nitrates. A soln. of N2O5 in dichloromethane added with stirring to ethylene oxide in the same solvent at 10-15°, and worked up after 5 min - glycol nitrate. Y 96%. F.e. inch 1,3-diol nitrates from oxetanes s. P. Golding et al.. Tetrahedron Letters 29, 2731 (1988). 

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