RHODIUM-CATALYZED HYDROFORMYLATIONS OF UNSATURATED NITROGEN-HETEROCYCLES - REGIOSELECTIVITY AND STEREOSELECTIVITY IN THE SYNTHESIS OF TROPANE AND PIPERIDINE CARBOXYALDEHYDES

Results of the RhH(CO)(PPh3)3-catalyzed hydroformylations of several unsaturated nitrogen heterocycles under moderate conditions are reported. Substrates included N-methyl-1,2,3,6-tetrahydropyridine, 8, N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, 9, N-ethoxycarbonyl-1,2,3,6-tetrahydropyridine, 10, tropidine, 11, 4-phenyltropidine, 12, and N-ethoxycarbonylnortropidine, 13. The relative reactivity was found to vary in the order: 13 > 11 .simeq. 10 > 8, with 12 and 9 being essentially unreactive. Conversion was high for the bicyclic olefins, 11 and 13, with the regio- and stereoselectivity favoring the symmetrical 3.beta.-carboxaldehyde isomers. Conversion was high for 10 with the regioselectivity favoring the unsymmetrical, 3-substituted isomer. Low conversion and little selectivity were observed in the reaction of 8. Olefin hydrogenation was extensive for substrate 8 only, and alcohol formation was a minor secondary reaction for all substrates. The temperature dependence of the product distributions is discussed along with results of competitive reactions between pairs of substrates.