Journal of the American Chemical Society, Vol.137, No.5, 1798-1801, 2015
Ruthenium-Catalyzed C-C Coupling of Amino Alcohols with Dienes via Transfer Hydrogenation: Redox-Triggered Imine Addition and Related Hydroaminoalkylations
Ruthenium-catalyzed hydrogen transfer from 4-aminobutanol to butadiene results in the pairwise generation of 3,4-dihydro-2H-pyrrole and an allylruthenium complex, which combine to form products of imine anti-crotylation. In couplings of 1-substituted-1,3-dienes, novel C2 regioselectivity is observed. As corroborated by deuterium labeling studies, kinetically preferred hydrometalation of the terminal olefin of the 1-substituted-1,3-diene delivers a 1,1-disubstituted p-allylruthenium complex that isomerizes to a thermodynamically more stable monosubstituted p-allylruthenium complex, which undergoes imine addition with allylic inversion through a closed transition structure. Direct ruthenium-catalyzed diene hydroaminoalkylations with pyrrolidine also are described.