Reactivity and selectivity in the cyclization of sila-5-hexen-1-yl carbon-centered radicals

摘要: Abstract A trio of sila-5-hexen-1-yl radicals has been prepared from the corresponding halides by reaction with tri- n -butyltin hydride (deuteride). The possessing a dimethylsilyl function α or β to carbon radical center demonstrated marked reduction in total (but especially exo-trig ) cyclization compared all-carbon system. γ-silyl behaved, contrariwise, quite comparably difference found α-silyl was result both pronounced decrease rate via expected mode and significantly enhanced hydrogen abstraction TBTH . Both α- cyclized endo-trig at rates close that parent 5-hexen-1-yl itself. cyclizations studied were be irreversible. kinetic control thus shown preferred formation endo product β-silyl is highly unusual represents first report carbon-centered type violating Baldwin-Beckwith rule radicals). Rationalization behavior involves steric electronic factors. most case, radical, which lowest propensity no exo product, remains largely unexplained because its unavailable as yet. Some speculative considerations involving conformation this system relation are given.