Synthesis and transformations of some N-substituted (1R,4S)-3-aminomethylidene-1,7,7-trimethylbicyclo [2.2.1]-heptan-2-ones

Acid-catalysed reactions of (1R,3E,4S)-3-[(dimethylamino)methylidene]-1,7,7-trimethylbicyclo[2.2.1]heptan2-one (2) with amino acid derivatives 3a-d and pyrazolidin-3-ones 5a-e gave the substitution products 4/4'a-d and 6a-e, respectively, in 40-83% yields. Compound 4a was transformed with Bredereck's reagent into the 3-(dimethylamino)propenoate 7/7'. Treatment of 1-{[(1R,32,45)-1,7,7-trimethyl-2-oxobicydo-[2.2.1]hept-3-ylide-ne]methyl}pyrazolidin-3-ones 6a and 6b with dimethyl acetylenedicarboxylate in refluxing anisole furnished the corresponding cycloadducts as mixtures of four diastereomers, the major endo-isomers 10/lla,b and the minor exo-isomers 12/13a,b with moderate curio-selectivity. Chromatographic separation of 10/11/12/13a,b afforded the endo/exo-pairs of diastereomers, 10/13a,b and 11/12a,b. The structures of compounds 4/4', 6, 7/7', and 10/11/12/13 were determined by NMR and by X-ray diffraction.