8 research outputs found
Mild and Ligand-Free Pd(II)-Catalyzed Conjugate Additions to Hindered Ī³-Substituted Cyclohexenones
Ligand-free cationic Pd(II) catalyst with NaNO<sub>3</sub> as an additive is a highly active catalytic system for conjugate additions to sterically hindered Ī³-substituted cyclohexenones. More challenging Ī³Ī³- and Ī²Ī³-substrates also react well to produce products with quaternary centers in good dr. The conjugate additions occur in a diastereoselective fashion under mild, practical and air-stable conditions, using readily available commercial reagents
Gold(I) and Palladium(II) Complexes of 1,3,4-Trisubstituted 1,2,3-Triazol-5-ylidene āClickā Carbenes: Systematic Study of the Electronic and Steric Influence on Catalytic Activity
The
synthesis of a small family of six electronically and sterically
modified 1,3,4-trisubstituted 1,2,3-triazol-5-ylidene goldĀ(I) chloride
complexes is described. Additionally, the corresponding <i>trans</i>-[PdBr<sub>2</sub>(iPr<sub>2</sub>-bimy)Ā(1,3,4-trisubstituted 1,2,3-triazol-5-ylidene)]
complexes are also generated and used to examine the donor strength
of the 1,3,4-trisubstituted 1,2,3-triazol-5-ylidene ligands. All compounds
have been characterized by <sup>1</sup>H and <sup>13</sup>C NMR and
IR spectroscopy, high-resolution electrospray mass spectrometry (HR-ESI-MS),
and elemental analysis. The molecular structures of four of the goldĀ(I)
and four of the palladiumĀ(II) complexes were determined using X-ray
crystallography. Finally, it is demonstrated that these 1,2,3-triazol-5-ylidene
goldĀ(I) chloride complexes (AuĀ(trz)ĀCl) are able to catalyze the cycloisomerization
of 1,6-enynes, in high yield and regioselectivity, as well as the
intermolecular direct etherification of allylic alcohols. Exploiting
the AuĀ(trz)Cl precatalysts allowed the etherification of allylic alcohols
to be carried out under milder conditions, with better yield and regioselectivity
than selected commercially available goldĀ(I) catalysts
Gold(I)-Catalyzed Addition of Thiols and Thioacids to 3,3-Disubstituted Cyclopropenes
GoldĀ(I)-catalyzed reactions of thiols, thiophenols, and
thioacids
with 3,3-disubstituted cyclopropenes occur in a regioselective and
chemoselective manner to produce either vinyl thioethers or primary
allylic thioesters in good yields. A survey of commonly used goldĀ(I)
catalysts shows Echavarrenās cationic goldĀ(I) catalyst to be
most tolerant of deactivation by sulfur. A novel digold with bridging
thiolate complex is characterized by X-ray crystallography, shedding
light on a possible deactivation pathway
Gold(I)-Catalyzed Addition of Thiols and Thioacids to 3,3-Disubstituted Cyclopropenes
GoldĀ(I)-catalyzed reactions of thiols, thiophenols, and
thioacids
with 3,3-disubstituted cyclopropenes occur in a regioselective and
chemoselective manner to produce either vinyl thioethers or primary
allylic thioesters in good yields. A survey of commonly used goldĀ(I)
catalysts shows Echavarrenās cationic goldĀ(I) catalyst to be
most tolerant of deactivation by sulfur. A novel digold with bridging
thiolate complex is characterized by X-ray crystallography, shedding
light on a possible deactivation pathway
Ligand- and Base-Free Pd(II)-Catalyzed Controlled Switching between Oxidative Heck and Conjugate Addition Reactions
A simple change of solvent allows controlled and efficient switching between oxidative Heck and conjugate addition reactions on cyclic Michael acceptor substrates, catalyzed by a cationic Pd(II) catalyst system. Both reactions are ligand- and base-free and tolerant of air and moisture, and the controlled switching sheds light on some of the factors which favor one reaction over the other
Ligand- and Base-Free Pd(II)-Catalyzed Controlled Switching between Oxidative Heck and Conjugate Addition Reactions
A simple change of solvent allows controlled and efficient switching between oxidative Heck and conjugate addition reactions on cyclic Michael acceptor substrates, catalyzed by a cationic Pd(II) catalyst system. Both reactions are ligand- and base-free and tolerant of air and moisture, and the controlled switching sheds light on some of the factors which favor one reaction over the other
Gold-Catalyzed Proto- and Deuterodeboronation
A mild
gold-catalyzed protodeboronation reaction, which does not
require acid or base additives and can be carried out in āgreenā
solvents, is described. As a result, the reaction is very functional-group-tolerant,
even to acid- and base-sensitive functional groups, and should allow
for the boronic acid group to be used as an effective traceless directing
or blocking group. The reaction has also been extended to deuterodeboronations
for regiospecific <i>ipso</i>-deuterations of aryls and
heteroaryls from the corresponding organoboronic acid. Based on density
functional theory calculations, a mechanism is proposed that involves
nucleophilic attack of water at boron followed by rate-limiting BāC
bond cleavage and facile protonolysis of a AuāĻ-phenyl
intermediate
Divergent Outcomes of Gold(I)-Catalyzed Indole Additions to 3,3-Disubstituted Cyclopropenes
Depending on the conditions employed, gold(I)-catalyzed addition of indoles to 3,3-disubstituted cyclopropenes can be controlled to yield either 3-(<i>E</i>)-vinylindoles (<b>3</b>) or <i>bis-</i>indolylalkanes (<b>4</b>). If the cyclopropene substituents are sterically bulky, unprecedented gold-catalyzed oxidation under air occurs to yield <i>bis</i>-indolylalkene (<b>5</b>) and epoxide (<b>6</b>) at room temperature