Ring opening pyrolytic

The strain of cycloproparenes is the principal obstacle that must be overcome in their synthesis. Cycloproparenes decompose usually at moderate temperatures, and they undergo ring-opening in the presence of electrophilic or metallic reagents. In contrast, they support even strongly basic conditions quite well. Accordingly, most successful cycloproparene syntheses use some base-induced elimination in the last step. Alternatively, flash vacuum pyrolytic or photochemical extrusion of a neutral fragment, followed by biradical closure or flash vacuum pyrolysis may be used. In these latter approaches the reaction conditions are neutral, and reactive products may be trapped at low temperatures. 

Electrochemical oxidation of adenine and hydroxyadenines in aqueous solution at pH 3-11.2 using a pyrolytic graphite electrode gave after extended oxidation, a diimine species which undergoes a series of reactions to give various ring-opened products <9UCS(P2)1369> (see Section 7.11.5.2.4). 

The 1-silacyclobutene side of this type of equilibrium was also reached by ring expansion in phenylcyclopropylsilylene obtained by pyrolysis of a silabenzonorborna-diene precursor (equation 106)223. Photochemical or pyrolytic ring opening of a l-silacyclobut-2-ene derivative provides an entry to the 1-silabutadiene series151. 

Selective V-alkylation or -alkenylation of pyrimidinethiones is difficult to achieve because of preferential reactivity of the sulfur with the electrophile. 5,V-Disubstitution proceeds readily, however, as in the formation of the 2,3-dihydrothiazolo[3,2-c]pyrimidinium-8-olates (477). The protons of the dihydrothiazolo ring are acidic, especially in the 3-position. Strong base abstraction of an //3-proton leads to ring-opening to the V-vinylpyrimidinone (479). The latter is also formed from the 3-carboxy derivative (478) by ready pyrolytic decarboxylation promoted by the adjacent pyrimidinium nitrogen atom <84JHC1149>. 

The production of pure (i )-(-)-linalool involves hydroperoxidation of (].R,2S,5R)-(+)-pinane by air oxygen the pinane enantiomer is obtained by eatalytie hydrogenation of (+)-a-pinene. Another catalytic hydrogenation eonverts the hydroperoxide to (l/ ,2i ,5/ )-(-)-2-pinanol which opens its eyelobutane ring by pyrolytic cycloreversion to the target compound with its pleasant flowery odor, widely used in perfumery instead of bergamot or French lavender. 

Pyrolytic ring opening Ethyleneoxo compounds from 2-(l -alkenyl)cycloalkanols... 

Without additional reagents Pyrolytic ring opening... 

The pyrolytic decomposition of the three point poly(borazinylamine) has been followed by TGA, thermal desorption mass spectrometry and isotope distribution analysis. Although the full details of the solid state decomposition and lamellar structure assembly are not yet revealed, it can be concluded that borazine ring opening is a crucial reaction at low temperatures and some degree of solid state lamellar order is found for samples heated between 400 C and 500 C. In fact, these samples show x-ray patterns similar to those shown in Fig. 1. High temperature pyrolysis is required to remove the last hydrogen atoms in this structure as well. The early stage of the decomposition is iUustrated schematically in Scheme n. 

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