Cyclisation of 5-Bromomethyl-Cycloheptene and -Cyclo-Octene: A New Route to Bicyclo[3.2.1]Octanes and Bicyclo[4.2.1]Nonanes

Reduction of 5-(bromomethyl)cycloheptene with tributyltin hydride gave bicyclo[3.2.1 ] octane; similar reduction of 5-(bromomethyl)cyclo-octene gave bicyclo[4.2.1 ]nonane together with some bicyclo[3.3.1 Jnonane. The cyclohept-4-enylmethyl radical intermediate exists as a rapidly equilibrating mixture of conformers, including the axial boat form from which cyclisation occurs. The rates of the two main cyclisation reactions are ca. 105 s_1 at 25 °C. Condensation of the dimethylamine enamine of 4-methylcyclohexanone with acrylaldehyde and subsequent treatment with methyl iodide and base gave 6-methyloctahydro-1 -benzopyran-2-one.