1,3-Cationic Alkylidene Migration of Nonclassical Carbocation: A Density Functional Theory Study on Gold(I)-Catalyzed Cycloisomerization of 1,5-Enynes Containing Cyclopropene Moiety

Cascade alkyl migration in 2-alkynylanilines for the synthesis of benzenoid ring multi-functionalized indoles

Cascade alkyl migration of 2-alkynylanilines via an aromaticity destruction and reconstruction process is reported. The first alkyl migration is triggered by generation of a dearomatized arenium species via oxidation and cyclization, and the second is driven by the force to restore the aromaticity of rearrangement products. The reaction gave rise to a range of multi-functionalized indoles.

Gold-Catalyzed Addition of β-Oxo Enols at Tethered Alkynes via a Non-Conia-ene Pathway: Observation of a Formal 1,3-Hydroxymethylidene Migration

With the relay process of Ag(I)/Au(I) catalysts, a one-pot synthesis of skeletally rearranged (1-hydroxymethylidene)indene derivatives from 2-alkynylbenzaldehydes and α-diazo esters is described. This cascade sequence involves Au(I)-catalyzed 5-endo-dig attack of highly enolizable aldehydes at the tethered alkynes, leading to carbocyclizations with a formal 1,3-hydroxymethylidene transfer. On the basis of density functional theory calculations, the mechanism likely involves formation of cyclopropylgold carbenes, followed by an appealing 1,2-cyclopropane migration.

Yb(OTf)3 catalyzed [1,3]-rearrangement of 3-alkenyl oxindoles

A Yb(OTf)₃ catalyzed [1,3]-rearrangement of 3-alkenyl oxindoles was achieved, affording a variety of multifunctional 3-ylideneoxindoles with good yields and Z/E selectivities (64%-89% yield, 78 : 22->99 : 1 Z/E). Importantly, an operationally simple, one-pot sequential catalytic synthesis of 3-ylideneoxindoles was also developed. Additionally, a cross [1,3]-rearrangement experiment and nonracemic transformation were also carried out, which indicated a concerted rearrangement mechanism of this methodology.

Understanding the reaction mechanism of gold-catalyzed reactions of 2,1-benzisoxazoles with propiolates and ynamides

The detailed reaction mechanisms of gold-catalyzed reactions of 2,1-benzisoxazoles with propiolates and ynamides have been investigated with the aid of density functional theory calculations.

Copper-Catalyzed Cycloisomerization of Cyclopropenylimine for Synthesis of Pyrroles

Copper-catalyzed cycloisomerization of 3-iminocyclopropenes for synthesis of pyrroles has been developed. The reaction allows regioselective construction of pyrroles with various substitution patterns, including fully substituted pyrroles. The method was successfully applied to synthesis of steroidal pyrroles as well as a N-fused pyrrole.

Ruthenium Catalyzed Rearrangement of Ene-cyclopropenes. Divergent Reaction Pathways

The reaction of ene-cyclopropenes with Cp*RuCl(cod) leads to alkenyl bicyclo[3.1.0]hexanes, bicyclo[4.1.0]heptanes, and bicyclo[5.1.0]octanes. This reaction involves a reverse regioselectivity in the cyclopropene opening than with gold chlorides. With gem-disubstituted cyclopropenes, a novel cycloisomerization based on ring-opening nucleophilic attack and rearrangement is observed. Alternatively, some gem-disubstituted cyclopropenes give dimerizations of the intermediate carbene.

Diastereospecific Gold(I)-Catalyzed Cyclization Cascade for the Controlled Preparation of N- and N,O-Heterocycles

The reaction of oxime-tethered 1,6-enynes with a cationic gold(I) catalyst demonstrates a great potential for the synthesis of a range of heterocycles in a diastereospecific fashion. The control of the configuration of the oxime and the alkene of the enyne moiety is the key to selectively obtain dihydro-1,2-oxazines, isoxazolines or dihydropyrrole-N-oxides as single diastereoisomers. As supported by DFT calculations, these cascade reactions proceed stepwise, by the intramolecular addition of the O or N atom of the oxime onto cyclopropyl gold(I) carbene intermediates. In this study, a rare [3,3]-sigmatropic rearrangement of nitrones is also observed.

Highly Strained Organogold Complexes and Their Gold- or Rhodium-Catalyzed Isomerizations

The synthesis and characterization of (NHC)(tricyclo[4.1.0.0^2,7 ]hept-1-yl)gold(I) compounds is reported. Several of these organometallic compounds could be obtained by transmetalation from the organolithium precursor to the corresponding (NHC)gold(I) chlorides. These are by far the most strained stable organogold compounds reported so far. With these new compounds we were able to efficiently and selectively accomplish the first gold-catalyzed rearrangement of organogold compounds, even better yields were obtained by the first rhodium-catalyzed rearrangement of these organogold species. (E/Z)-Mixtures of (NHC)(cyclohex-2-en-1-ylidenemethyl)gold(I) were obtained, none of the other known rearrangement products of tricycloheptanes. Additional insight into the chemical and physical properties of the strained compounds was obtained by spectroscopic and computational studies.

Sulfonyl radical-enabled 6-endo-trig cyclization for regiospecific synthesis of unsymmetrical diaryl sulfones

A new sulfonyl radical-triggered 6-endo-trig cyclization of unactivated 1,5-enynes under catalytic oxidation conditions for flexible synthesis of unprecedented unsymmetrical diaryl sulfones was established.

PtI2-catalyzed cyclization of 3-acyloxy-1,5-enynes with the elimination of HOAc and a benzyl shift: synthesis of unsymmetrical m-terphenyls

A new cyclization of 1,5-enyne was developed to synthesize the m-terphenyls via the elimination of HOAc and a benzyl shift.