ADDITION AND CYCLIZATION REACTIONS IN THE THERMAL-CONVERSION OF HYDROCARBONS WITH AN ENYNE STRUCTURE, 5 - HIGH-TEMPERATURE RING CLOSURES OF1,3-HEXADIEN-5-YNES TO NAPHTHALENES - COMPETING REACTIONS VIA ISOAROMATICS, ALKENYLIDENE CARBENES, AND VINYL-TYPE RADICALS

The 4-substituted 1-phenyl-1-butene-3-ynes 1a-c and the 2-ethynylstyre nes 7a-c were subjected to high-temperature pyrolysis. The cycloisomer ization products isolated suggest that these are formed by three compe ting processes: by (i) an electrocyclic or a molecule-induced, (ii) an alkenylidene carbene controlled, and (iii) a radical-controlled ring- closure process. To estimate the relative importance of these three re actions here mentioned, the substrates have been isomerized in oxygen- free nitrogen and in nitrogen proportionally substituted by toluene at 700 and 650 degrees C, respectively. The relative contributions of th ese isomerizations depend not only on the conversion temperature but a lso on the substituent R in 1 or 7.