The nature of the electronic factor governing diastereofacial selectivity in remotely substituted (X) 2‐adamantyl cations: 5‐X versus 4‐X substitution

Abstract

AbstractA limited series of 4eq‐substituted (X) 2‐methyleneadamantanes (6, YCH2, XF, Cl, Br, I, and SnMe3) has been synthesized and diastereoselectivities for their hydrochlorination (HCl/CH2Cl2) have been determined. Diastereoselectivities for the fluorination (DAST/CH2Cl2) of secondary alcohol mixtures, obtained from the hydride reduction of the precursor ketones (6,YO) to the alkenes, have also been measured. A comparison of this selectivity data for nucleophilic trapping of 4eq‐substituted (X) 2‐adamantyl cations (4, RH and Me) with the corresponding information for 5‐substituted (X) 2‐adamantyl cations (1, RH and Me) has revealed important distinctions between the two series. In particular, whereas extended hyperconjugative effects appear to be the predominant electronic effect governing facial selectivity in the 5,2‐series, electrostatic influences prevail in the 4,2‐disposition. Copyright © 2007 John Wiley & Sons, Ltd.