Origin of the preference for the chair conformation in the Cope rearrangement. Effect of phenyl substituents on the chair and boat transition states

Abstract

d,l- and meso-2,2'-bis[1-methylene-1,2,3,4-tetrahydronaphthalenes] 8 and 9 were synthesized, and the activation energy parameters for their unimolecular [3,3] sigmatropic rearrangement to 1,2-bis(3,4-dihydro-1-naphthalenyl)ethane (13) were determined. The d,l(diastereomer is constrained to undergo Cope rearrangement in the chair conformation while the meso diastereomer is constrained to the boat. At 150 o C k d,l /k meso =7×10 6