An unstrained homoallylic secondary adamantyl toluene-p-sulfonate solvolyses with σ-bond migration to give a protoadamantyl substituted allylic carbenium ion

Abstract

The aqueous ethanolysis of 4-adamantylidene-2_ax-adamantyl toluene-p-sulfonate (tosylate) (1a–OTs) shows a sensitivity (m value) of 0.86 ± 0.05 to the ionizing power of the solvent. 1a–OTs reacts approximately 4.7-fold faster than 2-adamantyl tosylate in 80∶20 v/v ethanol–water at 25 °C. The solvolysis reactions of 1a–OTs result in complete (>95%) rearrangement of the substituted adamantyl ring into a protoadamantyl ring via a solvent-equilibrated allylic carbenium ion intermediate. The extrapolated α-secondary deuterium kinetic isotope effect for solvolysis of 1a–OTs in 60∶40 v/v ethanol–water at 25 °C is 1.16 ± 0.02, while comparable values for solvolysis of the epimeric 2_eq tosylate 1e–OTs measured in several ethanol–water mixtures at 25 °C fall in the range 1.14–1.17. These results are consistent with a 1a–OTs solvolysis reaction transition state that involves concerted σ-bond participation and departure of the tosylate leaving group.