Titanium-catalyzed cycloaddition reactions of phenyl(trimethylsilyl)acetylene to conjugated dienes and 1,3,5-cycloheptatriene. 1-Phenyl-2-(trimethylsilyl)-cyclohexa-1,4-dienes and their aromatization

The catalytic system Et 2 AlCl/TiCl 4 induces Diels-Alder addition of phenyl(trimethylsilyl)acetylene (PTMSA) to 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-methyl-1,3-pentadiene, and [6+21 addition of PTMSA to 1,3,5-cycloheptatriene. The 1-phenyl-2-(trimethylsilyl)-cyclohexa-1,4-dienes obtained undergo thermolysis, yielding the corresponding ortho -(trimethylsilyl)biphenyl derivatives. The cyclohexadienes containing vicinal methyl and trimethylsilyl groups evolve methane at 300°C (the 3-methyl group is released). All other derivatives release hydrogen at only 260°C.