Heating with silver nitrate in aqueous acetone under reflux gave only starting material. Similar complex mixtures and poor yields were observed on repeating the above sequence with the dibromocarbene adduct 2b . The tricyclic ketones 3 proved more interesting from a synthetic viewpoint. Two stereoisomeric products were obtained in good yield, and easily distinguished by n.m.r. spectroscopy. The nucleophile is thus delivered to the exo surface of the developing electrophile.
All compounds are racemic.
M.p.s were determined on an Electrothermal apparatus and are uncorrected. Unless otherwise stated, i.r. spectra were of liquid paraffin mulls on sodium chloride plates, recorded on Perkin-Elmer 257 or 297 spectrometers. Mass spectra were measured on a Kratos MS30 instrument with a 70 eV electron impact source, and the peak abundances are quoted as a percentage of the base peak. Organic solutions were dried using anhydrous magnesium sulphate and concentrated by rotary evaporation. Petroleum' refers to light petroleum, b.p.