Stereoselectivity in the intramolecular Pauson-Khand reaction: Towards a simple predictive model

Regio- and Diastereoselective Tandem Rhodium-Catalyzed Allylic Alkylation/Pauson−Khand Annulation Reactions

“…We envisioned an alternative approach to this problem that utilized a single metal-catalyst to facilitate both transformations in a tandem sequence, using only the reaction temperature to modulate the catalytic activity. The obvious advantage of this strategy was the ability to significantly increase the molecular complexity of the bicyclic adduct through the introduction of a stereogenic center at C-2, which we anticipated would control diastereoselectivity in the PK annulation . Herein, we now describe the development of the regio- and diastereoselective rhodium-catalyzed tandem allylic alkylation/Pauson−Khand annulation reaction using stabilized carbon and heteroatom nucleophiles (eq 1).…”

The Phenylsulfonyl Group as anendo Stereochemical Controller in Intramolecular Pauson–Khand Reactions of 3-Oxygenated 1,6-Enynes

“…[14] Although the assumed multistep mechanism of the PK reaction makes rationalization of the stereochemical outcome difficult, two main factors are usually invoked in diastereoselective PK cyclizations: the conformational preferences of the starting complex prior to metallacycle formation [7,15] and the thermodynamic stability of the putative key cis-cobaltacycle intermediates. [2,16] In the case of the 1-sulfonylated-1,6enynes, both effects could operate in the same direction, providing a reasonable explanation for the observed major formation of the endo isomer (Scheme 2). Thus, as we had Scheme 2.…”

The PAUSON-KHAND REACTION IN SYNTHESIS OF BICYCLIC RIGID Α-Amino ACIDS

“…Thus it has been found that high stereoselectivity may be achieved in 3,4-and 4,5-disubstituted 1,6-heptenynes, and that the selectivity is influenced by the nature and relative stereochemistry of the substituents. 17,18 The stereoisomers 3 and 4 were readily separated by flash chromatography and were obtained in crystalline state. Their structures and relative stereochemistry at C-5 0 in the bicyclo[3,3,0]octane moiety have been established by single crystal x-ray analysis, as given in formulae 3 and 4.…”