A typical example of rate acceleration by F-strain in solvolysis

Abstract

The new bridgehead triflates or mesylates were synthesized for the Z and E forms of the 2-ethylidenebicyclo[2.2.2]oct-l-yl (3), 2-ethylidene-l-adamantyl (5), and 2-ethylidenebicyclo[3.2.2]non-1-yl (7) systems, and their Z/E rate ratios at 25 °C compared in the solvolysis in ethanol or 2,2,2-trifluoroethanol (TFE). The Z/E rate ratios are 217 for 3-0Tf in EtOH and 126 for 5-OMs in TFE, suggesting the marked F-strain in such rigid 1 systems. Contrarily, the Z/E rate ratio for rather flexible 7-OMs is 0.30, demonstrating the importance of a rigid structure for exerting the F-strain. Molecular mechanics and AMI calculations supported the rate data.