318
Bimolecular Eliminations in Conformationally Biased Systems Containing Acidic ,B Protons. The 2-( p-Tolylsulfonyl) -4-t-butylcyclohexylSulfonates’ W. M. Jones,2 T. G . squire^,^ and Merrill Lynn
Contributionf r o m the Department of Chemistry, University of Florida, Gainesville, Florida 32601. Received September 14, 1966 Abstract: The four possible configurational isomers of 2-(p-tolylsulfonyl)-4-t-butylcyclohexanolhave been synthesized. Configurational assignments to these four alcohols depend on their method of synthesis, the desulfurization of one to its corresponding 4-t-butylcyclohexanol, and their interrelation in ethoxide-catalyzed epimerizations. The assignments are dramatically confirmed by the nmr splitting patterns of the sulfone and sulfonate methine hydrogens of the sulfonate esters. The rates of piperidine-induced elimination from the sulfonate esters of three of these alcohols as well as the sulfonates of cis- and trans-2-p-tolylsulfonylcyclohexanol were determined in dimethylformamide solvent. It was found that in some cases, added piperidine hydrochloride caused a small but real rate retardation. However, deuterium exchange studies showed that this retardation is not due to reversible carbanion formation. It was further found that the rates of elimination from the different isomers are relatively insensitive to the nature of the leaving group (p-toluenesulfonate US. methanesulfonate), the dihedral angle between the leaving group and the acidic hydrogen (of the 2-arylcyclohexyl sulfonate^^^), and even the cis-trans relationship between the leaving group and the acidic hydrogen (except in the cases where an anti-periplanar conformation is present in the ground state). All of these observations point to a mechanism in which heterolysis of the carbonoxygen bond to the leaving group plays at most a minor role in the rate-determining step. However, it is not possible to conclude from these data that a carbanion is formed as a distinct intermediate.
E
limination reactions involving loss of a relatively acidic proton have been the subject of considerable interest over recent years. These investigations have almost invariably focused on the possibility of observing an E l c B elimination mechanism5 and have utilized H
I
-C-C-
1
‘ X
+B:
k-1
kl
1 I x I
e
-C-C-
L+
kz
+ B’-H >c=c
