A Pauson-Khand approach to the synthesis of ingenol

[reaction: see text] Pauson-Khand cyclization of dioxanone photoadduct 21 leads to the formation of a single product in good yield. However, retro-aldol fragmentation of the pentacyclic cyclopentenone 22 leads to the formation of 23, with cis C-8/C-10 intrabridgehead stereochemistry, unlike the target compound ingenol 1, which possesses C-8/C-10 trans intrabridgehead stereochemistry.     

An allenic Pauson-Khand approach to 6,12-guaianolides

Cyclocarbonylation of α-methylene butyrolactone-containing allene-ynes affords 6,12-guaianolide ring systems. Incorporation of the α-methylene butyrolactone early in a synthetic sequence is rare for reactivity reasons; however, this moiety proves to be beneficial to the allenic Pauson-Khand reaction. The three double bonds and the ketone in the resulting 5-7-5 ring system bear significant differences in their reactivity and are ideally positioned for synthetic application to 6,12-guaianolides and analogs.     

New approach to indole alkaloids based on the intramolecular Pauson-Khand reaction

The synthesis of indoles bearing alkenyl and alkynyl moieties in different positions of the nucleus is described. These compounds are used as substrates for the intermolecular Pauson-Khand reaction leading to tetracyclic cyclopentenones with formation of additional five- to seven-membered rings. Products are related to alkaloids such as mitosenes, clausines, ergotamines, or apogeissochizines.     

Heterobimetallic alkyne complexes in organic synthesis: An asymmetric variant of the Pauson-Khand reaction

The use of heterobimetallic alkyne complexes for the synthesis of cyclopentenones is described. The inherent chirality of the complexes has been used to effect high levels of stereocontrol in transformations giving optically enriched organic end products.     

A Pauson-Khand approach to the hamigerans

An intramolecular Pauson-Khand reaction has been used in the construction of the tricyclic core common to the hamigeran terpenes. For effective cyclization, it was necessary to tether the olefin-containing moiety to the aromatic framework to reduce its conformation mobility; this was accomplished using a silylene protecting group. Efficient construction of the aryl enyne from a salicylic acid derivative was accomplished via ortho lithiation and Sonogashira cross-coupling chemistry.     

An efficient catalytic protocol for the Pauson-Khand reaction

New experimental conditions have been developed for an efficient catalytic Pauson-Khand reaction. These are based on the use of a mixture of molecular sieves and tert-butanol as inducers of the process. This mixture, with the appearance of a paste, is able to adsorb CO, thus improving the conversion and making it possible to effect the reactions in the absence of a CO atmosphere. The protocol is applied to known and unknown substrates and compared to previously described conditions, showing good results with intra- and intermolecular examples.     

Rhodium catalyzed asymmetric Pauson-Khand reaction using SDP ligands

~~Rhodium catalyzed asymmetric Pauson-Khand reaction using SDP ligands1. Khand, I. U., Knox, G R., Pauson, P. L. et al., Organocobalt complexes, Part Ⅱ. Reaction of acetylenehexacarbonyldicobalt complexes, (R1C2R2)Co2(CO)6, with norbomene and its deri…     

A facile synthesis of the basic steroidal skeleton using a Pauson-Khand reaction as a key step

A high-yield synthesis of steroid-type molecules under mild reaction conditions is achieved in two steps involving nucleophilic addition of alkynyl cerium reagent to an easily enolizable carbonyl compound (beta-tetralone) followed by an intramolecular Pauson-Khand reaction.     

N-phosphino-p-tolylsulfinamide ligands: synthesis, stability, and application to the intermolecular Pauson-Khand reaction

Here we synthesized a family of racemic and optically pure N-phosphino-p-tolylsulfinamide (PNSO) ligands. Their stability and coordination behavior toward dicobalt-alkyne complexes was evaluated. Selectivities of up to 3:1 were achieved in the ligand exchange process with (mu-TMSC2H)Co2(CO)6. The resulting optically pure major complexes were tested in the asymmetric intermolecular Pauson-Khand reaction and yielded up to 94% ee. X-ray studies of the major complex 18a indicated that the presence of an aryl group on the sulfinamide reduces the hemilabile character of the PNSO ligands.     

The intermolecular Pauson-Khand reaction

Five membered carbocycles are important building blocks for many biologically active molecules. Moreover, substituted cyclopentenones (e.g. cyclopentenone prostaglandins) exhibit characteristic biological activity. The efficiency and atom economy of the Pauson-Khand reaction render this process potentially one of the most attractive methods for the synthesis of such compounds. Although it was discovered in its intermolecular form, the scope of the intermolecular Pauson-Khand reaction has always been limited by the poor reactivity and selectivity of the alkene component. The past decade, especially the last three years, has seen concerted efforts to broaden the scope of this reaction. In this overview, we provide a comprehensive and critical coverage of the intermolecular Pauson-Khand reaction based on the reactivity characteristics of different classes of alkenes and a rationalization of successes and misfortunes in this area.     

Short synthesis of methylenecyclopentenones by intermolecular Pauson-Khand reaction of allyl thiourea

N,N,N′-Trimethylallylthiourea promotes the intermolecular Pauson-Khand reaction with alkynes in the presence of Co₂(CO)₈ and moderate pressure of CO followed by thiourea elimination allowing the formation of methylenecyclopentenone derivatives.     

Cobalt-phosphite-catalyzed asymmetric Pauson-Khand reaction

A complex formed from dicobalt octacarbonyl and a chiral aryl bisphosphite served as a catalyst for the intramolecular asymmetric Pauson-Khand reaction. Bicyclic cyclopentenones were obtained in up to 75% enantiomeric excess. For a terminal 1,6-enyne, the incremental enantiomeric excess was found to increase from 4 to 26% over the course of the reaction. The scope of this process was examined for a variety of 1,6- and 1,7-enynes, and a moderate degree of enantioselectivity was maintained only in the case of aryl-substituted 1,6-enynes.     

Pauson-Khand反应的研究进展

综述了过渡金属络合物参与或催化的Pauson-Khand反应，不对称Pauson- Khand反应的最新进展。     

An intramolecular Tsuji-Trost reaction based approach to the synthesis of 6-methylene indolizidines

Herein we describe the efficient stereoselective preparation of C8 substituted indolizidines bearing a 6-methylene group, from the chiral pool starting material l-proline. This synthesis, employing a Tsuji-Trost reaction as the key step, represents a potentially, efficient route to pumiliotoxin natural product epimers.     

The Pauson-Khand reaction, a powerful synthetic tool for the synthesis of complex molecules

There are still some synthetic chemists who hesitate to use metal-mediated or -catalysed reactions. The Pauson-Khand reaction (PKR) is a powerful transformation that has now been sufficiently well developed to be routinely considered when planning a synthesis, especially of polycyclic complex molecules. This tutorial review aims to encourage the use of this process explaining the best ways of performing a PKR both in the stoichiometric and the catalytic version, showing the scope of the process and its limitations. Additionally, asymmetry can be introduced in the reaction using several strategies, which will be discussed. The most recent examples of the synthetic applications of the PKR in natural product synthesis will give the reader an idea of the great usefulness of this reaction.     

Stereoselective synthesis of spiroannulated cyclopentenones by the Pauson-Khand reaction on carbohydrate derived enynes

The stereoselective synthesis of spiroannulated cyclopentenones by the Pauson-Khand reactions on hexose and pentose derived enynes was achieved under carbon monoxide free conditions using a stoichiometric quantity of Co₂(CO)₈. The cobalt complex of the alkyne was cleaved using dimethoxyethane-acetonitrile at 85 °C to furnish spiroannulated cyclopentenones in 75-94% yields.     

Catalyst precursors for the catalytic Pauson-Khand reaction

Dicobalt hexacarbonyl complexes of enynes serve as Co₂(CO)₈ surrogates for the intramolecular Pauson-Khand cycloaddition. Enynes with polar functional groups allow for easy separation of the catalyst cyclopentenone by-product (acid or base wash, silica gel plug column) from the desired cyclopentenone.