Synthesis and Transformations of Some N-Substituted (1R,4S)-3-Aminomethylidene-1,7,7-trimethylbicyclo[2.2.1]- heptan-2-ones

Uroš Grošelj, Simon Rečnik, Anton Meden, Branko Stanovnik*, and Jurij Svete*

Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, P.O. Box 537,
1000 Ljubljana, Slovenia

Acid-catalysed reactions of (1
R,3E,4S)-3-[(dimethylamino)methylidene]-1,7,7-trimethylbicyclo[2.2.1]heptan-2-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,3Z,4S)-1,7,7-trimethyl-2-oxobicyclo-[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 10/11a,b and the minor exo-isomers 12/13a,b with moderate endo-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.

Key words: camphor, enaminones, condensations, pyrazolidin-3-ones, pyrazolo[1,2–a]pyrazoles