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
π-allylruthenium complex that isomerizes to a thermodynamically
more stable monosubstituted π-allylruthenium complex, which
undergoes imine addition with allylic inversion through a closed transition
structure. Direct ruthenium-catalyzed diene hydroaminoalkylations
with pyrrolidine also are described.