Barriers to intramolecular hydride transfers in some polycyclic hydroxyketones

Abstract

The hydroxyketones (1) and (2) have been prepared from the Diels–Alder adducts of p-benzoquinone with cyclopentadiene and cyclohexa-1,3-diene. The boron trifluoride–ether catalysed reaction of cyclohepta-1,3-diene with p-benzoquinone gave good yields of the Diels–Alder adduct which was converted into hydroxyketone (3). Experiments with cyclohexanol and admantan-2-ol established characteristic 13C n.m.r. chemical shifts associated with deprotonation of alcohols by dimsyl sodium in dimethyl sulphoxide. Solutions of the sodium salts of (1)–(3) were prepared and dynamic 13C n.m.r. spectroscopy gave barriers for their degenerate rearrangement of >21.7 (100 °C), 19.0 (100 °C), and 17.3 (72 °C) kcal mol–1, respectively. The relationship between variation of barrier and molecular geometry is discussed with the aid of empirical force field calculations.