Gold-Catalyzed Ring Research Articles

Construction of Cyclic Nitrones Enabled by Photodriven and Gold-Catalyzed 1,3-Azaprotio Transfer of Allenyloximes.

A protocol was developed to construct five- to seven-membered cyclic nitrones through the gold-catalyzed 1,3-azaprotio transfer of allenyloximes under photoirradiation. The photoisomerization of oximes was suggested to convert the inert stereoisomer to a reactive one. This photodriven and gold-catalyzed ring formation could be further extended to the thermodynamically stable aryl ketoximes with an E-configuration, which previously displayed chemical inertness in the absence of light irradiation.

Gold-Catalyzed Ring Expansion Reaction: Highly Efficient Synthesis of Functionalized 2, 3-Benzodiazepine Scaffolds

Gold-Catalyzed Ring Expansion Reaction: Highly Efficient Synthesis of Functionalized 2, 3-Benzodiazepine Scaffolds

Gold-Catalyzed Ring Expansion of Enyne-Lactone: Generation and Transformation of 2-Oxoninonium.

An efficient gold-catalyzed ring-expansion reaction of enyne-lactones to form 2-oxoninonium intermediates is reported. The 2-oxoninonium generated in this work could undergo further 6π electrocyclization and aromatization reaction to produce different aromatic compounds.

Kinetic or Dynamic Control on a Bifurcating Potential Energy Surface? An Experimental and DFT Study of Gold-Catalyzed Ring Expansion and Spirocyclization of 2-Propargyl-β-tetrahydrocarbolines.

In classical transition state theory, a transition state is connected to its reactant(s) and product(s). Recently, chemists found that reaction pathways may bifurcate after a transition state, leading to two or more sets of products. The product distribution for such a reaction containing a bifurcating potential energy surface (bPES) is usually determined by the shape of the bPES and dynamic factors. However, if the bPES leads to two intermediates (other than two products), which then undergo further transformations to give different final products, what factors control the selectivity is still not fully examined. This missing link in transition state theory is founded in the present study. Aiming to develop new methods for the synthesis of azocinoindole derivatives, we found that 2-propargyl-β-tetrahydrocarbolines can undergo ring expansion and spirocyclization under gold catalysis. DFT study revealed that the reaction starts with the intramolecular cyclization of the gold-activated 2-propargyl-β-tetrahydrocarboline with a bPES. The cyclization intermediates can not only interconvert into each other via a [1,5]-alkenyl shift, but also undergo ring expansion (through fragmentation/protodeauration mechanism) or spirocyclization (through deprotonation/protodeauration mechanism). Detailed analysis of the complex PESs for substrates with different substituents indicated that the reaction selectivity is under dynamic control if the interconversion of the intermediates is slower than the ring expansion and spirocyclization processes. Otherwise, the chemical outcome is under typical kinetic control and determined by the relative preference of ring expansion versus spirocyclization pathways. The present study may enrich chemist's understanding of the determinants for selectivities on bPESs.

Formation and isomerization of polycyclic 1,5-enynes

A 1,5-enyne with the alkyne flanked by a cyclopropane and a cyclobutane, formed by intramolecular [2+2] photocycloaddition of a pyridone with an enyne, undergoes gold catalyzed ring closure to give a cyclopentene, without isomerization of either small ring. The ring closure can also be effected by thiol radical conditions. The chemistry of the resulting tetracycle with its five stereogenic centers, has been studied.

ChemInform Abstract: Azocinoindole Synthesis by a Gold(I)‐Catalyzed Ring Expansion of 2‐Propargyl‐β‐tetrahydrocarboline.

AbstractGold‐catalyzed ring enlargement of N‐propargylated β‐tetrahydrocarbolines offers a general approach to 1H‐azocino[5,4‐b]indoles.

Gold-Catalyzed Formation of Oxonium Ions from Enynes and Their Intra- and Intermolecular Trapping with Allylsilanes

Gold-catalyzed ring closure of 1,5-enyne containing a silyl ether at the allylic position induces a skeletal rearrangement to form an oxonium intermediate, which then undergoes a smooth allylation in both an intra- and intermolecular manner. In the intramolecular allyl transfer, the additive alcohol becomes positioned on the silicon of the silyl ether by forming a new Si-OR bond, whereas, in the intermolecular allylation, the alcohol is incorporated in the homoallylic carbon by forming a C-OR bond.

ChemInform Abstract: Synthetic Applications of Gold‐Catalyzed Ring Expansions

AbstractReview: 64 refs.

Synthetic applications of gold-catalyzed ring expansions.

The development of new methodologies catalyzed by late transition metals involving cycloisomerizations of strained rings can open new venues for the synthesis of structurally complex molecules with interesting biological activities. Herein we summarize, from both a synthetic as well as a mechanistic point of view, the most recent developments in gold-catalyzed ring expansions.

Counterion Effects in a Gold-Catalyzed Synthesis of Pyrroles from Alkynyl Aziridines

Aryl-substituted N-tosyl alkynyl aziridines undergo a gold-catalyzed ring expansion to afford 2,5-substituted pyrrole products. Under certain conditions, a ring-expansion and rearrangement leads to 2,4-substituted pyrroles. The reaction pathway is determined by the counterion to the gold catalyst.