Generation of Cyclopenta[c]piperidines and Pyrrolo[3,4-c]piperidines—Potential Substance P Antagonists—from Adducts of Cyclic Dienophiles and 5-Chloro-6-methyl-3-phenyl-2H-1,4-oxazin-2-one

1,1,4,4-Tetrasubstituted cyclopenta[c]piperidines and the corresponding 4,4,7,7-pyrrolo[3,4-c]piperidines have been synthesised via cycloaddition of 5-chloro-6-methyl-3-phenyl-2H-1,4-oxazin-2-one with cyclopentene and 3-pyrroline derivatives, respectively, followed by reductive opening of the lactone-bridged adducts. The axial-equatorial conformational preferences of the substituents in these cis-fused bicyclic systems were opposite to those for the monocyclic piperidine analogues. The specific array of functional groups in the bicyclic aminoalcohols was used to accommodate, in stereocontrolled fashion, variable pharmacophoric groups that are of interest for substance P antagonist activity.