Addition and cyclization reactions in the thermal conversion of hydrocarbons with an enyne structure, 5: High-temperature ring closures of 1,3-hexadien-5-ynes to naphthalenes - Competing reactions via isoaromatics, alkenylidene carbenes, and vinyl-type radicals

Article abstract of DOI:10.1002/jlac.199719971218

The 4-substituted 1-phenyl-1-butene-3-ynes 1a-c and the 2-ethynylstyrenes 7a-c were subjected to high-temperature pyrolysis. The cycloisomerization products isolated suggest that these are formed by three competing processes: by (i) an electrocyclic or a molecule-induced, (ii) an alkenylidene carbene controlled, and (iii) a radical-controlled ring-closure . To estimate the relative importance of these three reactions here mentioned, the substrates have been isomerized in oxygen-free nitrogen and in nitrogen proportionally substituted by toluene at 700 and 650°C, respectively. The relative contributions of these isomerizations depend not only on the conversion temperature but also on the substituent R in 1 or 7. Wiley-VCH Verlag GmbH, 1997.