Abstract
Abstract: A series of 7-azabicyclo[2.2.1]hept-5-ene complexes are prepared from [Os(NH3)s(?72-L)]2+ (L= pyrrole,
1-methylpyrrole, 2,5-dimethylpyrrole, 1,2,5-trimethylpyrrole, or l-(trimethylsilyl)pyrrole) and various dipolarophiles
(e.g., acrylonitrile, methyl acrylate, -methylene-y-butyrolactone, dimethyl maleate, dimethyl fumarate, W-phenyl
maleimide, cyclopentene-1,2-dicarboxylic acid anhydride, and (E)- and (Z)- methyl 3-(3'-pyridyl)acrylate). The
cycloaddition is promoted by coordination of the pyrrole with [Os(NH3)s]2+ across C3 and C4, transforming the
uncoordinated portion of the pyrrole nucleus into an azomethine ylide capable of undergoing 1,3-dipolar cycloadditions.
The metal serves not only to activate the pyrrole ring but also to stabilize the resulting 7-azabicyclo[2.2.1 ]heptene
ligands. A number of organic 7-azabicyclo[2.2.1]heptanes, including analogs of the alkaloid epibatidine, have been
synthesized by this methodology. For the cases examined, the cycloaddition favors exo stereochemistry of the electron-
withdrawing substituent when the pyrrole nitrogen is unsubstituted. Crystal structures have been determined for the
complexes obtained from the reactions of pyrrole with W-phenylmaleimide (8a), 2,5-dimethylpyrrole with dimethyl
maleate (13a), and 2,5-dimethylpyrrole with -methylene-y-butyrolactone (22a).
