REDUCTIVE TRANS-2,6-DIALLYLATION OF PYRIDINES WITH ALLYLBORANES - SYNTHESIS OF TRANS-2,6-DIALLYL-1,2,5,6-TETRAHYDROPYRIDINES AND CIS-2,6-DIALLYL-1,2,5,6-TETRAHYDROPYRIDINES AND THEIR DEUTERATED DERIVATIVES

The reductive trans-2,6-diallylation of pyridines with triallyl- and allyI(dialkyl)boranes has been discovered. Heating (40-100 degrees C) of pyridine, deuteropyridine, or 3-bromopyridine complexes with triallylborane in the presence of alcohols (ROH or CH3OD), water, or Et(2)NH results in the respective trans-2,6-diallyl-1,2,5,6-tetrahydropyridines (2, 3, 22, or 25) In 20-97% yields. A preparative method for the isomerization of trans-2,6-diallyl compounds 2 and 25 into the respective cis-isomers 4 and 28 by heating them with triallyl- or allyl(dialkyl)boranes (125-150 degrees C) has been suggested. The hydrogenation of trans- or cis-2,6-diallyl-1,2,5,6-tetrahydropyridines gave trans- or cis-2,6-dipropylpiperidines, respectively. The cis- and trans-configurations of compounds 2 and 4 were established by analyzing the NMR spectra of N-benzyl (7 and 13) and N,N-dimethyl (6 and 14) derivatives of piperidine derivatives 5 and 8. A possible mechanism for the reductive diallylation of pyridines has been discussed.