Structural analysis of cis-[n.3.1]bicyclic ketones by x-ray crystallography. Impact of the observed conformational crossover by .pi.-facially diastereoselective nucleophilic additions to this class of ketones and on the stereochemical course of electrophilic reactions involving their methylene analogs - Paquette, Leo A; Underiner, Ted L; Gallucci, Judith C (Journal of organic chemistry, 1992)