Gold-catalyzed cycloisomerizations of enynes: a mechanistic perspective

Addition of lithiated methoxyallene to aziridines – a novel access to enantiopure piperidine and β-amino acid derivatives

Addition of lithiated methoxyallene to aziridine derivatives provided the expected primary addition products. The less substituted carbon of the aziridine ring was attacked selectively. The primary adducts could be converted to enantiopure piperidine derivatives or β-amino acid derivatives. The unexpected reactions lead to a tricyclic sulfonamide and to alkynyl-substituted aminoethers. The efficient two-step conversion of a piperidone derivative to a benzomorphan demonstrates the potential of this approach to biologically active compounds.

Gold-catalyzed reactions of 1,5- and 1,6-enynes with carbonyl compounds: cycloaddition vs. metathesis

Gold and rings: The gold(I)-catalyzed addition of aldehydes to 1,6-enynes gives 1,3-dienes, by a cycloaddition/fragmentation process. 1,5-Enynes react with aldehydes and ketones by the 5-endo-dig pathway to give the corresponding cycloadducts.

Synthesis and structural characterisation of stable cationic gold(I) alkene complexes

Treatment of [AuCl(PBu(t)(3))] with AgSbF(6) in CH(2)Cl(2) at room temperature in the presence of the alkenes norbornene, norbornadiene, trans-cyclooctene, and also interestingly, isobutylene, leads to the formation of stable crystalline complexes [Au(PBu(t)(3))(alkene)][SbF(6)], characterised by NMR spectroscopy and X-ray crystallography.

Ligand-controlled access to [4 + 2] and [4 + 3] cycloadditions in gold-catalyzed reactions of allene-dienes

By adjustment of the electronic properties of the ancilliary ligands, high selectivity can be achieved for either [4 + 2] or [4 + 3] cycloaddition reactions of allene-dienes catalyzed by gold(I). Triarylphosphitegold(I) complexes are employed as catalysts for a [4 + 2] cycloaddition reaction leading to alkylidenecyclohexenes. Conversely, di-tert-butylbiphenylphosphinegold(I)-catalyzed reactions afford cycloheptadienes via [4 + 3] cycloaddition reactions.

Carbocyclisation of alkynes with external nucleophiles catalysed by gold, platinum and other electrophilic metals

This tutorial review covers recent developments in catalytic carbocyclisation of functionalised alkynes with external nucleophiles catalysed by gold, platinum and other electrophilic metals. Substrates of such reactions require a tethered functionality to react with the alkyne to complete a carbocyclic ring. We classify the reactions according to the tethered functionalities to illustrate the diversity of the carbocyclisations; these substrates include: (1) alkyne-alkyne, (2) alkyne-allene, (3) alkyne-alkene, (4) oxo-alkynes and (5) oxo-diynes and triynes. Besides their mechanistic interest, these reactions meet atom economy criteria because complex and functionalised carbocyclic products are easily assembled in a cascade sequence from readily available alkynes and nucleophiles.

Mechanistic studies on Au(I)-catalyzed [3,3]-sigmatropic rearrangements using cyclopropane probes

A comparative study of the Au(I)-catalyzed [3,3]-sigmatropic rearrangement of propargylic esters and propargyl vinyl ethers is described. Stereochemically defined cyclopropanes are employed as mechanistic probes to provide new synthetic and theoretical data concerning the reversibility of this type of rearrangement. Factors controlling the structure-reactivity relationship of Au(I)-coordinated allenes have been examined, thereby allowing for controlled access to orthogonal reactivity.

Au(I)-Catalyzed cycloisomerizations terminated by sp(3) C-H bond insertion

The gold(I)-catalyzed cycloisomerization of 1,5-enynes and 1,4-allylallenes to tetracyclododecane and tetracyclotridecane derivatives, respectively, is reported. Complexation of the cationic gold(I) complex to either the alkyne or allene moiety induces an intramolecular addition of the alkene, leading to a gold(I)-stabilized carbenoid intermediate. This intermediate undergoes a formal sp(3) C-H insertion to generate the tetracyclic adduct. A series of deuterium labeling experiments showed that the C-H functionalization step proceeds with an inverse kinetic isotope effect.

Asymmetric synthesis of medium-sized rings by intramolecular Au(I)-catalyzed cyclopropanation

An efficient method for the asymmetric gold(I)-catalyzed preparation of medium sized rings has been developed. The method provides 7- to 9-membered rings in excellent yield. High enantioselectivities can be achieved for 7- and 8-membered ring products employing chiral gold(I) complexes. The results provide insight into the mechanism, showing the fluxional nature of gold(I)-stabilized vinyl carbenoid intermediates.