6 research outputs found
Mechanistic Study of the Direct Intramolecular Allylic Amination Reaction Catalyzed by Palladium(II)
DFT calculations (PBE1PBE/6-31GÂ(d,p),
Def2-TZVPPD) were performed
to study the intramolecular CâH amination of an unsaturated
carbamate catalyzed by [PdÂ(LL)Â(OAc)<sub>2</sub>] (<b>2</b>),
where LL is the bisÂ(sulfoxide) ligand PhSÂ(O)Â(CH<sub>2</sub>)<sub>2</sub>SÂ(O)ÂPh. The coordination takes place by an associative path over
a trigonal-bipyramidal transition state. The LL ligand undergoes a
coordination shift from Îș<sup>2</sup>S,S to Îș<sup>1</sup>S, leaving an open position for binding of the substrate (Cî»C).
In the next step, the CâH activation, the transition state
for the hydrogen abstraction from the substrate to form the Ï-allyl
complex has an energy of 124.0 kJ mol<sup>â1</sup>, which is
the highest energy in the whole mechanism (TOF-determining transition
state). The Ï-allyl converts easily in the Ï-allyl, the
acetic acid molecule leaving the coordination sphere. The remaining
acetate receives the second hydrogen from the NH group, while the
newly formed acetic acid molecule is replaced by the pendant arm of
the LL ligand, and the cyclization takes place (nucleophilic attack).
During these changes, the metal is reduced to Pd(0) in the form of
the Pd(0) complex of the oxazolidinone product, the most stable species
in the cycle (TOF-determining intermediate). Either the CâH
activation or the Pd(0) oxidation may be the step determining the
energy span of the reaction, depending on reaction conditions
Palladium-Catalyzed Arylic/Allylic Aminations: Permutable Domino Sequences for the Synthesis of Dihydroquinolines from MoritaâBaylisâHillman Adducts
An efficient palladium-catalyzed synthesis of 1,2-dihydroquinolines has been developed via the reaction between anilines and MoritaâBaylisâHillman adducts derived from <i>o</i>-bromobenzaldehyde. This new Pd(0)-catalyzed pseudo-domino type I sequence involves a BuchwaldâHartwig arylic amination and an allylic amination. When starting from an <i>o</i>-bromo allylic alcohol, the chronology is arylic amination/allylic arylation. However, the sequence reverses when the reaction is performed on the corresponding <i>o</i>-bromo allylic acetate
Pd-Catalyzed Direct CâH Alkenylation and Allylation of Azine <i>N</i>âOxides
A Pd-catalyzed direct
C<sub>2</sub>-alkenylation of azine <i>N</i>-oxides with
allyl acetate is disclosed. The products are
formed through an allylation/isomerization cascade process. The use
of a tri-<i>tert</i>-butylphosphonium salt as the ligand
precursor and KF is mandatory for optimal yields. When cinnamyl acetate
is used, the same catalytic system promotes C<sub>2</sub>-cinnamylation
of the azine <i>N</i>-oxide without subsequent isomerization.
A mechanism is proposed on the basis of experimental studies and DFT
calculations
Opening the Way to Catalytic Aminopalladation/Proxicyclic Dehydropalladation: Access to Methylidene ÎłâLactams
A new aerobic intramolecular palladiumÂ(II)-based
catalytic system
that triggers aminopalladation/dehydropalladation of <i>N</i>-sulfonylÂalkenylamides to give the corresponding methylidene
Îł-lactams has been identified. Use of triphenylphosphine and
chloride anion as ligands is mandatory for optimal yields, and molecular
oxygen can be used as the sole terminal oxidant. Scope and limitations
of the methods are described. A mechanism is proposed on the basis
of experimental results as well as density functional theory calculations
Opening the Way to Catalytic Aminopalladation/Proxicyclic Dehydropalladation: Access to Methylidene ÎłâLactams
A new aerobic intramolecular palladiumÂ(II)-based
catalytic system
that triggers aminopalladation/dehydropalladation of <i>N</i>-sulfonylÂalkenylamides to give the corresponding methylidene
Îł-lactams has been identified. Use of triphenylphosphine and
chloride anion as ligands is mandatory for optimal yields, and molecular
oxygen can be used as the sole terminal oxidant. Scope and limitations
of the methods are described. A mechanism is proposed on the basis
of experimental results as well as density functional theory calculations
Palladium-Catalyzed [3 + 2]-CâC/NâC Bond-Forming Annulation
The synthesis of
bi- and tricyclic structures incorporating pyrrolidone
rings is disclosed, starting from resonance-stabilized acetamides
and cyclic α,ÎČ-unsaturated-Îł-oxycarbonyl derivatives.
This process involves an intermolecular TsujiâTrost allylation/intramolecular
nitrogen 1,4-addition sequence. Crucial for the success of this bis-nucleophile/bis-electrophile
[3 + 2] annulation is its well-defined step chronology in combination
with the total chemoselectivity of the former step. When the newly
formed annulation product carries a properly located <i>o</i>-haloaryl moiety at the nitrogen substituent, a further intramolecular
keto α-arylation can join the cascade, thereby forming two new
cycles and three new bonds in the same synthetic operation