Reductive allylation of pyrrole with allylboranes. Synthesis of trans- andcis-2,5-disubstituted pyrrolidines

Pyrrole undergoes reductive mono- and diallylation on successive treatment with beta,gamma-unsaturated organoboron derivatives (triallylborane, allyl( dipropyl)borane, and triprenylborane) and alcohols to give 2-allylated 3-py rrolines and trans-2,5-diallylated pyrrolidines. The addition of both the f irst and second boron-allylic fragment to the heterocycle proceeds with rea rrangement. A method for transformation of the trans-2,5-diallylpyrrolidine into the cis-isomer (heating with triallylborane at 190 degrees C) was dev eloped and a series of N-substituted derivatives of these pyrrolidines was synthesized. A method for the preparative synthesis of nonsymmetrically sub stituted trans- and cis-2-alkyl(phenyl)-5-allylpyrrolidines, based on reduc tive allylboration of pyrrole followed by 1,2-addition of RLi to the 5-ally l-1-pyrroline that formed, was also developed. A direct confirmation of int ermediate formation of 2H- and 3H-pyrrole tautomers under the action of all ylboranes was obtained. The adduct of 2H-pyrrole with BF3 was detected by N MR spectroscopy.