Pd-Catalyzed Asymmetric Cyclopropanation Reaction of Acyclic Amides with Allyl and Polyenyl Carbonates. Experimental and Computational Studies for the Origin of Cyclopropane Formation

Cyclopropanes
with three chiral centers were afforded in good to
high yields with dr ratio of 4–23:1 and ee of 83–99%
in the reaction of acyclic amides with monosubstituted allyl carbonates
as well as polyenyl carbonates under the Pd-catalysis in the presence
of (Sphos,R)-SIOCPhox L1 as the ligand, while allylic alkylated products were provided
only if (Rphos,R)-SIOCPhox L2 was the ligand. The amide group of product was easily reduced
to hydroxymethyl group in high yield. The active reaction intermediate
was determined and transition states for cyclopropanation and allylation
were calculated. The origin of cyclopropane formation was investigated
by experiments, NMR studies, X-ray analysis of allyl-Pd-ligand complexes,
and DFT calculations.