Ethylene derivs., cyclic trans

On the other hand, cis or trans and cyclic 1,2-disubstituted ethylenes have been well-known till 1980 to be not homopolymerized with a radical initiator owing to the much more increased steric effect of the substituents except for a few exceptions, e.g., fluoro-substituted ethylenes and cyclic derivatives, vinylene carbonate (VCa), maleic anhydride (MAn), yV-substituted maleimides (RMI), and acenaphthylene. However, if 1,2-disubstituted and tri- or tetra-substituted ethylenes can homopolymerize, the polymers with a substituted polymethylene structure, which is different from the above polyethylenes, would be obtained (eqs. 1 and 2), i.e., the polymers would be less flexible (more rigid), and have higher glass transition temperatures than those for the polyethylenes, although their processabilities would decrease. 

The products of the thermolysis of 3-phenyl-5-(arylamino)-l,2,4-oxadiazoles and thiazoles have been accounted for by a radical mechanism.266 Flash vacuum pyrolysis of 1,3-dithiolane-1 -oxides has led to thiocarbonyl compounds, but the transformation is not general.267 In an ongoing study of silacyclobutane pyrolysis, CASSF(4,4), MR-CI and CASSCF(4,4)+MP2 calculations using the 3-21G and 6-31G basis sets have modelled the reaction between silenes and ethylene, suggesting a cyclic transition state from which silacyclobutane or a trans-biradical are formed.268 An AMI study of the thermolysis of 1,3,3-trinitroazacyclobutane and its derivatives has identified gem-dinitro C—N bond homo lysis as the initial reaction.269 Similar AMI analysis has determined the activation energy of the formation of NO2 from methyl nitrate.270 Thermal decomposition of nitromethane in a shock tube (1050-1400 K, 0.2—40 atm) was studied spectrophotometrically, allowing determination of rate constants.271... 

In our retrosynthetic analysis (Scheme 19), we envisioned that the penta-cyclic skeleton common to perophoramidine (77) and communesins (78) could be constructed via silver-mediated Diels-Alder reaction of a tryptamine derivative 74 with benzodiene 73 generated in situ from chloroaniline 72. We postulated two stereochemical outcomes for the proposed Diels-Alder reaction (a) exo addition via transition state 75 would generate a perophoramidine-like intermediate 77 with two trans ethylene groups at C7 and C8, or (b) endo addition via transition state 76 would yield a communesin-like pentacyclic intermediate 78 with two cis ethylene groups at C7 and C8. Since the success of our planned DA reaction depended on synthesizing the benzodiene precursor 72, our first task was to prepare this compound from isatin. 

Heating 1,4,5,6-tetra-O-benzyl-myo-inositol with ethylene carbonate and a trace of sodium bicarbonate affords the 2,3-cyclic carbonate derivative. The reaction fails where there is a trans-diol arrangement as with 1,2,3,6-tetra-O-benzyl-myo-inositol. ... 

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