Stereoselective reductive tetraallylation of pyridinecarboxylic acids withtriallylborane

Reductive tetraallylation of pyridine-3- and pyridine-4-carboxylic acids wi th triallylborane in the presence of propan-2-ol proceeded stereoselectivel y to yield trans-2,6-diallyl-3- and trans-2,6-diallyl-4-(1-allyl-1-hydroxyb ut-3-en-1-yl)-1,2,5,6-tetrahydropyridines, respectively. Under the same con ditions, the reaction with pyridine-2-carboxylic acid gave a mixture of tra ns- and cis-2,6-diallyl-2-(1-allyl-1-hydroxybut-3-en-1-yl)-1,2, 5,6-tetrahy dropyridines in a ratio of 57 : 43. When 2,6-diphenylpyridine-4-carboxylic acid reacted with triallylborane, only the carboxylic group underwent reduc tive diallylation. When heated with triallylborane in o-xylene (130-133 deg rees C, 7 h), trans-2,6-diallyl-4-(1-allyl-1-hydroxybut-3-en-1-yl)1,2,3,6-t etrahydropyridine was converted to the corresponding cb-isomer. The stereoc hemistry of trans-2,6-diallyl-3-(1-allyl-1-hydroxybut-3-en-1-yl)-1,2,5,6-te trahydropyridine was confirmed by X-ray diffraction analysis.