title: Gas-phase facial diastereoselectivity of equatorial and axial 4-chloro-adamant-2-yl cations.
abstract: The acid-catalyzed addition of CH3(18)OH to 2-methylene-adamantanes bearing a chlorine atom in the 4-equatorial (1e) or 4-axial (1a) position has been investigated in the gas phase, at 760 Torr, in the 40-120 degrees C temperature range. Two different experimental approaches were employed: (1) by adding neutral CH3(18)OH to the 2-methyl-4-Cl-adamant-2-yl cation, generated by protonation of the corresponding 2-methylene-4-Cl-adamantane (the extracomplex reaction) and (2) by reaction of 2-methylene-4-Cl-adamantane with CH3(18)OH2+, generated by methylation of H2(18)O (the intracomplex reaction). The crucial role of the nature of the noncovalent intermediates involved along the reaction coordinates emerges from the difference between the results obtained in the extracomplex and intracomplex reactions for both substrates investigated. The kinetic and stereochemical results indicate that the 4-Cl substituent plays a different role depending on its equatorial or axial orientation. Examination of the experimental results in the light of MP2/6-31G* theoretical calculations provides important information about the intrinsic factors governing the facial diastereoselectivity of trigonal carbocations. The effects due to differential face solvation phenomena emerge from the comparison of the present gas-phase results with those obtained from strictly related studies in solution.
authors.affiliation: Dipartimento di Chimica e Tecnologie del Farmaco, Università di Roma La Sapienza, P.le A. Moro, 5, Roma 00185, Italy.
authors.forename: Caterina
authors.initials: C
authors.lastname: Fraschetti
authors.forename: Francesca R
authors.initials: FR
authors.lastname: Novara
authors.forename: Antonello
authors.initials: A
authors.lastname: Filippi
authors.forename: Maurizio
authors.initials: M
authors.lastname: Speranza
authors.forename: Neil A
authors.initials: NA
authors.lastname: Trout
authors.forename: William
authors.initials: W
authors.lastname: Adcock
authors.forename: Enrico
authors.initials: E
authors.lastname: Marcantoni
authors.forename: Gabriele
authors.initials: G
authors.lastname: Renzi
authors.forename: Graziella
authors.initials: G
authors.lastname: Roselli
authors.forename: Mauro
authors.initials: M
authors.lastname: Marcolini