Journal of the American Chemical Society p. 7723 - 7732 (1989)
Update date:2022-08-04
Topics:
Leardini, Rino
Nanni, Daniele
Pedulli, Gian Franco
Tundo, Antonio
Zanardi, Giuseppe
et al.
The 1,2 migration of the aryl group in deuterated 2-(9-anthryl)ethyl and 2-<9-(10-phenylanthryl)>ethyl radicals has been studied by product analyses with the use of the competing reaction ArCH2CD2(.) + Bu3SnH.The rearrangement was so fast that equimolecular mixtures of the unrearranged (ArCH2CD2H) and rearranged (ArCD2CH3) hydrocarbons were obtained even in the presence of a large excess of Bu3SnH (ca. 1 M).The lower limit for the rate constant of the intramolecular process, kr, could be estimated as 5E7 s-1.Ab initio MO computations, performed on the2-phenylethyl radical, chosen as the simplest model for 2-arylethyls, showed that the aryl migration may occur either through the intermediacy of the spirocyclopropanecyclohexadienyl radical or via a three-membered transition state having geometrical and electronic properties different from those of the potential cyclic intermediate.The spectroscopic and chemical results are consistent with the rearrangement taking place via the intermediacy of spirocyclopropane radicals, which, as both thermochemical calculations and experimental evidence indicate, are characterized by a considerable thermodynamic stability.In fact, the spiro radicals could be easily observed by EPR spectroscopy when generated by hydrogen abstraction from the corresponding cyclic hydrocarbons, and the kinetics of their decay could be studied.The diamagnetic dimer of the 9,10-dihydro-10-spiro
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