Novel Kumada coupling reaction to access cyclic (2-azaallyl)stannanes. Cycloadditions of cyclic nonstabilized 2-azaallyllithium species derived from cyclic (2-azaallyl)stannanes.
A Kumada cross-coupling reaction involving organomagnesium reagents and (3-methylthio-2-azaallyl)stannanes with a Ni(0) catalyst provided cyclic nonstabilized (2-azaallyl)stannanes in moderate to good yields. Primary alkyl, aryl, and allylic organomagnesium reagents can be used as the cross-coupling partner. In general, NiCl(2)dppp in toluene at room temperature provided the shortest reaction times and most consistent yields. The azomethine ylides and 2-azaallyllithium species derived from these stannanes were shown to undergo efficient [3 + 2] cycloaddition reactions to provide azabicyclo[n.2.1]alkanes as the endo cycloadducts. These cycloadducts were found to be useful as starting materials for further elaboration into aza-bridged bicyclic natural and unnatural products of biological interest. Although cyclic 2-azaallyllithium species have been generated previously, this work reports the first generation and cycloaddition of entirely nonstabilized 2-azaallyllithium species. In addition a novel extension of the Kumada coupling was developed to allow for the preparation of the cyclic (2-azaallyl)stannanes, which are precursors to the nonstabilized 2-azaallyllithium species.
Mans
Douglas M
DM
Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, USA.
Pearson
William H
WH
D008094:Lithium / Q000737:chemistry*; D017971:Tin Compounds / Q000737:chemistry*
D017971:Tin Compounds; C031525:stannane; D008094:Lithium