LASER-POWERED DECOMPOSITION OF SPIRO[2.N]ALKANES (N = 2-5)

The laser heating of spiro[2.n]alkanes (n = 2-5) and of their 1,1,2,2- tetradeuterated isotopomers reveals dissimilar modes of their thermal decomposition. Spiropentane decomposes into ethene and propadiene via two competing routes: the direct cleavage and the more important cleav age via intermediary methylenecyclobutane. Spirohexane decomposes thro ugh two important concurrent pathways which are the expulsions of ethe ne from the three-membered ring and a more feasible expulsion of ethen e from the four-membered ring. Spiroheptane and spirooctane decompose by a radical-chain mechanism and afford complex mixtures of products; upon addition of propene both compounds rearrange into two cycloalkane s wherein the larger ring of the spiroalkane is preserved and substitu ted with ethylidene and a vinyl group.