2 research outputs found
Total Synthesis of (<i>R</i>)‑Sarkomycin via Asymmetric Rhodium-Catalyzed Conjugate Addition
(<i>R</i>)-Sarkomycin was prepared using a five-step
total synthesis. Key steps in the enantioselective construction of
the targeted scaffold were a rhodium-catalyzed asymmetric conjugate
alkenyl addition with subsequent silyl trapping and a Mukaiyama aldol
reaction with aqueous formaldehyde. Protection of the hydroxy group
as a THP acetal and oxidative cleavage of the C,C-double bond provided
a stable direct precursor to the natural product. The final liberation
was carried out under slightly acidic conditions in a microwave-assisted
reaction, resulting in a high yield of the “deceptive”
sarkomycin. This represents the shortest enantioselective synthesis
of this rather unstable compound to date and the first to employ asymmetric
catalysis to introduce the stereogenic center
Rhodium-Catalyzed Enantioselective Addition of Organoaluminum Reagents to <i>N</i>‑Tosyl Ketimines
Rhodium(I)/Binap complexes catalyze
highly enantioselective additions
of methyl- and arylaluminum reagents to cyclic α,β-unsaturated <i>N</i>-tosyl ketimines. Depending on the solvent and substituents
at the ring, the reaction occurs either in a 1,2-manner to deliver
α-tertiary allylic amines or in a 1,4-manner to yield, after
subsequent reduction, 3-substituted cycloalkyl amines. Well known
in the case of the respective cycloalkenones, these first transformations
of the aza-analogues enable the synthesis of amine structures of pharmaceutical
and biochemical interest