Aromatization cleavage, thermal

Aromatization by thermal cleavage Thiazoles from a-(2-/d -thiazolinyl)ketones... 

Finally the chemical aromatization of Ring A which occurs in nature in the biosynthesis of estrogens must be mentioned. It can be done by thermal cleavage of the C-19 methyl group in 1,4-dien-3-ones (H.H. Inhoffen, 1940 C. Djerassi, 1950) and was later achieved at lower temperatures with lithium — biphenyl in THF (H.L. Dryden, Jr., 1964). 

We have studied the thermal decomposition of diaryl ether in detail, since the cleavage of ether linkage must be one of the most responsible reactions for coal liquefaction among the various types of decomposition reaction and we found that the C-0 bond of polynucleus aromatic ethers is cleaved considerably at coal liquefaction temperature. 

THERMAL CLEAVAGE OF BENZYLIC BONDS IN AROMATIC SYSTEMS... 

Other approaches to alkylidenecycloproparenes have been attempted without success. Aromatization of appropriate alkylidenecyclopropanes or their precursors could not be realized, and flash vacuum pyrolysis of methylene phthalide and 3-methylene-2-coumaranone afforded rearrangement products rather than alkylidenecycloproparenes via extrusion of 002. The photochemical or thermal decomposition of the sodium salt of benzocyclobutenone p-toluenesulfonyl hydrazone led to products derived from dimerization of the intermediate benzocy-clobutenylidene, or from its reaction with the solvent, but no ring-contracted products were observed. When the adduct of methylene-l,6-methano[10]annulene to dicyanoacetylene (249) was subjected to Alder-Rickert cleavage, phenylacety-lene (250) was formed, which derives reasonably from the parent 234. ... 

The synthetically most valuable intermediate in heterofullerene chemistry so far has been the aza[60]fulleronium ion C59N (28). It can be generated in situ by the thermally induced homolytic cleavage of 2 and subsequent oxidation, for example, with O2 or chloranil [20-24]. The reaction intermediate 28 can subsequently be trapped with various nucleophiles such as electron-rich aromatics, enolizable carbonyl compounds, alkenes and alcohols to form functionalized heterofullerenes 29 (Scheme 12.8). Treatment of 2 with electron-rich aromatics as nucleophilic reagent NuH in the presence of air and excess of p-TsOH leads to arylated aza[60]fullerene derivatives 30 in yields up to 90% (Scheme 12.9). A large variety of arylated derivatives 30 have been synthesized, including those containing cor-annulene, coronene and pyrene addends [20, 22-25]. 

Naphthenes may undergo ring cleavage or side chain removal when thermally cracked. Longer side chain naphthenes are the most susceptible to side chain removal by thermal cracking. Aromatic compounds are the most resistant to thermal cracking conditions. The ease by which various hydrocarbons are cracked thermally can be ranked as follows ... 

The method of choice for the prefixation of the aromatic halves is the very practicable esterification reaction. This type of bridge ideally fulfills the requirements demanded easy formation, high thermal stability, good electronic coupling conditions, and, finally, facile cleavage by saponification or reduction. The chiral biaryls are thus obtained as biscarboxylic acids or bisbenzyl alcohols, respectively. 

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