Condensed cyclic and bridged-ring systems. Part IV. Stereochemically controlled synthesis of some endo-2-aryl-6-oxobicyclo[3.2.1]octanes and related compounds through intramolecular alkylations of γδ-unsaturated α′-diazomethyl ketones

Abstract

The 4-arylcyclohex-3-enecarboxylic acids (4a—d), prepared through a modified Diels–Alder reaction, have been converted via the corresponding diazomethyl ketones (5a—d) into cyclopropyl ketones (6a—d) and the 2-aryl-6-oxobicyclo[3.2.1]oct-2-ene derivatives (7a—d), by oxo-carbenoid addition and boron trifluoride–ether-catalysed cyclisation, respectively, in excellent yields. In addition to the unsaturated ketones (7a and c), the hydroxy-ketones (10a and c) were also obtained in the aqueous tetrafluoroboric acid-catalysed cyclisation of the diazoketones (5a and c). Catalytic reduction of the cyclopropyl ketones and the unsaturated ketones produced the endo-2-aryl-6-oxobicyclo[3.2.1]octane derivatives (8a—d) exclusively.