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

Some aspects of radical chemistry in the assembly of complex molecular architectures

This review article describes briefly some of the radical processes developed in the authors' laboratory as they pertain to the concise assembly of complex molecular scaffolds. The emphasis is placed on the use of nitrogen-centred radicals, on the degenerate addition-transfer of xanthates, especially on its potential for intermolecular carbon-carbon bond formation, and on the generation and capture of radicals through electron transfer processes.

Total synthesis of (-)-jiadifenin

As easy as ABCD: (-)-Jiadifenin was synthesized in eighteen reaction steps from 1-[(E)-(4'-bromo-2'-butenyl)oxy]-4-methoxybenzene. Key features of this synthesis include: 1) Ireland-Claisen rearrangement to produce the two contiguous quaternary centers at C5 and C6 simultaneously, 2) intramolecular Pauson-Khand reaction (IMPKR) to concurrently construct the A and B rings, and 3) [2+2] photo-cycloaddition to generate the all-carbon quaternary center at C9.

Asymmetric intramolecular Pauson-Khand reaction mediated by a remote sulfenyl or sulfinyl group

In this work, we report the use of the asymmetric intramolecular Pauson-Khand reactions of 4-aryl-4-cyano-1,6-enynes for obtaining enantiomerically enriched bicyclo[3.3.0]octenones, and the influence of both the quaternary stereocenter and the sulfur functions located at ortho-position of the aryl group, on their stereoselectivity and reactivity. The sulfenyl derivatives bearing substituted or unsubstituted triple bonds and mono- and disubstituted alkene moieties afford bicyclo[3.3.0]octenones in high yields with complete diastereocontrol. These results are explained by assuming the association of the lone electron pair at sulfur to the Co-alkyne complexes.

Carbonylation of 1-lithiobutadiene with carbon monoxide followed by intramolecular acyllithiation of C═C double bond and intermolecular acylation with acid chloride: scope, applications, and mechanistic aspects

The carbonylation of a 1-lithio-1,3-butadiene derivative with CO gave rise to a butadienyl acyllithio intermediate, which underwent an immediate intramolecular acyllithiation of the C═C double bond, affording a lithio cyclopentadienyl enolate. The X-ray structural analysis of the enolate revealed a dimer connected with a "Li(2)O(2)" four-membered ring. Subsequent intermolecular acylation of this enolate with acid chlorides afforded β-keto-3-cyclopentenones, γ-keto-2-cyclopentenones, or cyclopentadienyl ester derivatives. The stereo- and regioselectivity of the in situ generated lithio cyclopentadienyl enolate with various acid chlorides was investigated and analyzed, showing that the formation of the above products was significantly dependent on both the substituents on the butadienyl skeleton and the bulkiness of acid chlorides.

Scalable, stereocontrolled total syntheses of (±)-axinellamines A and B

The development of a simple, efficient, scalable, and stereocontrolled synthesis of a common intermediate en route to the axinellamines, massadines, and palau'amine is reported. This completely new route was utilized to prepare the axinellamines on a gram scale. In a more general sense, three distinct and enabling methodological advances were made during these studies: (1) an ethylene glycol-assisted Pauson-Khand cycloaddition reaction, (2) a Zn/In-mediated Barbier-type reaction, and (3) a TfNH(2)-assisted chlorination-spirocyclization.

Rh(I)-catalyzed intramolecular [2 + 2 + 1] cycloaddition of allenenes: Construction of bicyclo[4.3.0]nonenones with an angular methyl group and tricyclo[6.4.0.0]dodecenone

The [RhCl(CO)dppp]₂-catalyzed intramolecular carbonylative [2 + 2 + 1] cycloaddition of allenenes was developed to prepare bicyclo[4.3.0]nonenones possessing a methyl group at the ring junction, which is difficult to achieve by the Pauson–Khand reaction of the corresponding enynes. This method also provided a new procedure for the construction of the tricyclo[6.4.0.0^1,5]dodecenone framework in a satisfactory yield.