Transformations of pyridine and deuteropyridine under the action of trimethallylborane and alcohols. Synthesis of trans- and cis-2,6-dimethallyl-1,2,3,6-tetrahydropyridines and their N-derivatives

Reductive trans-2,6-dimethallylation of pyridine and deuteropyridine with trimethallylborane in the presence of alcohols proceeds at room temperature, i.e., under substantially milder conditions than the analogous reaction with the participation of triallylborane. trans-2,6-Di(2-methylallyl)-1 ,2,3,6-tetrahydropyridine (3) was obtained in a yield of 87%. When heated with trimethallylborane (130-135 degrees C, 2.5 h), compound 3 underwent isomerization to cis-2,6-di(2-methylallyl)-1,2,3,6-tetrahydropyridine (4). Hydrogenation of trans-(3) and cis-isomers (4) yielded trans-and cis-2,6-diisobutylpiperidines, respectively. The heterocycles obtained were N-functionalized by reactions with Mel, PhCH2Cl, ethylene oxide, and perfluoropropyloxirane. The stereochemistry of the cis-and trans-isomers (3 and 4) was established based on the NMR spectra of their N,N-dimethyl salts and the products of the reaction with ethylene oxide. trans-2,6-Dimethallyl-2,3,4,5,6-pentadeutero,2,3, 6-tetrahydropyridine and a number of its derivatives were prepared from the complex of trimethallylborane with C5D5N A probable mechanism of the reductive trans-2,6-diallylation of pyridines with allylboranes in the presence of alcohols is discussed.