Relative Rates and Arrhenius Parameters for Selected 1,2-Arylmigrations and Five- and Six-Member Cyclizations

摘要

The temperature dependent rates of radical rearrangements relative to abstraction of hydrogen atom from tri-n-butyltin hydride have been determined. The rearrangement of 2-phenyl-2-methylpropyl to 1-pheyl-2-methylpropyl (neophyl rearrangement) relative to hydrogen abstraction is represented by log r = 2.16 +- 0.08 - (7.48 +- 0.16)/THETA, THETA = 2.3RT kcal/mole. The rearrangement of o-allylbenzyl to 2-indanylmethyl exhibited log r = 2.24 +- 0.08 - (10.20 +- 0.25)/THETA, and the rearrangement of o-allylbenzyl to 2-tetralyl is represented by log r = (2.17 +- 0.13) - (12.32 +- 0.27)/THETA. The rearrangement of l-indanylmethyl to 2-tetralyl is represented by log r = 2.65 +- 0.06 - (11.21 +- 0.12)/THETA. The attempt to determine the cyclization rate of o-vinyl-2-phenylethyl radical to l-indanylmethyl and l-tetrlyl failed due to irreversible addition of tri-n-butyltin radical to the styrene double bond and other undefined competing reactions. However, kinetic closure to the five member ring was preferred over closure to the six member ring by roughly l kcal/mole. From known or estimated rates of abstract of hydrogen from tri-n-butyltin hydride, rates of rearrangement of the three radicals are derived. (ERA citation 09:014361)