Rhodium-catalyzed hydroformylations of unsaturated nitrogen heterocycles: regio- and stereoselectivity in the synthesis of tropane and pdperidine carboxaldehydes

Abstract

Results of the RhH(CO)(PPh 3) 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-tetrahydro-pyridine, 10, tropidine, 11, 4-phenyltropidine, 12, and N-ethoxycarbonyl-nortropidine, 13. The relative reactivity was found to vary in the order: 13 $ ̆ 11⋍ 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 3β-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.