4 research outputs found
A Formal Synthesis of (â)-Perhydrohistrionicotoxin Using a Cross MetathesisâHydrogenation Approach
The
development of an efficient, high yielding six-step convergent
synthesis of the semisynthetic alkaloid (â)-perhydrohistrionicotoxin
is described. The key transformations include the cross metathesis
of a Brønsted-acid masked primary homoallylic amine with a vinyl
cyclohexenone and a regioselective palladium catalyzed hydrogenation.
This sequence generated the advanced Winterfeldt spirocyclic precursor
in 47% overall yield, with a longest linear sequence of five steps
Influence of Phosphoramidites in Copper-Catalyzed Conjugate Borylation Reaction
CopperÂ(I) has become the preferred metal to catalyze
the β-boration
of ι,β-unsaturated carbonyl compounds, and now we demonstrate
that easily accessible monodentate chiral ligands, such as phosphoramidites
and phosphites, can be convenient alternative ligands to induce asymmetry
in the enantioselective version of this reaction, particularly in
the β-boration of ι,β-unsaturated imines
Lutidine-Derived Ru-CNC Hydrogenation Pincer Catalysts with Versatile Coordination Properties
Lutidine-derived
bis-N-heterocyclic carbene (NHC) ruthenium CNCâpincer
complexes (Ru-CNCâs) were prepared. Depending on the synthetic
procedure, normal (<b>1</b>, <b>2</b>) or mixed normal/abnormal
NHC-complexes (<b>3</b>) are formed. In the presence of phosphazene
base, Ru-CNC complexes activate nitriles to give ketimino compounds <b>4</b>â<b>6</b>. Nitrile adduct <b>4</b> shows
reactivity toward strong bases to yield dearomatized complex <b>7</b>, which heterolytically activates H<sub>2</sub> to form the
bis-hydrido complex <b>8</b>. Finally, these Ru-CNCâs
are active in catalytic hydrogenation of CO<sub>2</sub> to formate
salts, and unlike the phosphine-containing Ru-PNP counterpart, they
also catalyze the selective hydrogenation of esters to alcohols
Bis-N-heterocyclic Carbene Aminopincer Ligands Enable High Activity in Ru-Catalyzed Ester Hydrogenation
Bis-N-heterocyclic carbene (NHC)
aminopincer ligands were successfully
applied for the first time in the catalytic hydrogenation of esters.
We have isolated and characterized a well-defined catalyst precursor
as a dimeric [Ru<sub>2</sub>(L)<sub>2</sub>Cl<sub>3</sub>]ÂPF<sub>6</sub> complex and studied its reactivity and catalytic performance. Remarkable
initial activities up to 283âŻ000 h<sup>â1</sup> were
achieved in the hydrogenation of ethyl hexanoate at only 12.5 ppm
Ru loading. A wide range of aliphatic and aromatic esters can be converted
with this catalyst to corresponding alcohols in near quantitative
yields. The described synthetic protocol makes use of air-stable reagents
available in multigram quantities, rendering the bis-NHC ligands an
attractive alternative to the conventional phosphine-based systems