Diastereoselectivity Pauson-Khand reaction

Scheme 7. A diastereoselective Pauson-Khand reaction using a chiral-modified substrate according to M. A. Pericas.

Scheme 8. Diastereoselective Pauson-Khand reaction via diastereomerically pure alkyne complex...

A concise (10 steps) and efficient (12% overall yield) synthesis of ( )-13-deoxyserratine (203) has been achieved starting from an amidyl radical (101). The key reactions employed include the stereocontroUed introduction of the four stereogenic centers at C-4, C-7, C-12, and C-15. A diastereoselective Pauson-Khand reaction (102)... 

An enantioselective intramolecular Pauson-Khand reaction based on chiral auxiliary-directed 7t-face discrimination in acetylenic 0-alkyl enol ether-dicobalt hexacarbonyl complexes, which proceeds with good yields and high facial diastereoselectivity, has recently been developed by M.A. Pericas, A. Moyano, A.E. Greene and their associates. The method has been applied to an enantioselective formal synthesis of hirsutene. Moreover, the process is stereodivergent and the chiral auxiliary -rran5-2-phenylcyclohexanol- is recovered in a yield as high as 92% [18]. 

The Ir-tolBINAP catalyst also functions well in the desymmetrization of dienynes, where a highly enantioselective and diastereoselective Pauson-Khand-type reaction proceeded to give vinyl-substituted bicyclic cyclopentenones with two chiral centers (Scheme 11.19) [31]. 

The complex of o-substituted anisole 203 is planar chiral, and can be used for diastereoselective generation of two new stereogenic centres in the products. Propargylation and allylation of 203 gave 204 regio- and stereoselectively. Hydrolysis of 204 afforded the cyclohexenone 205, and its intramolecular Pauson-Khand reaction gave 206 diastereoselectively. The two reactions were completely diastereoselective, and the planar chirality in 203 was efficiently transferred to the three new stereogenic centers in 206 [51]. 

In the laboratory of S.L. Schreiber, the total synthesis of (+)-epoxydictymene was accomplished by the tandem use of cobalt-mediated reactions as key steps. The eight-membered carbocycle was formed via a Nicholas reaction, while the five-membered ring was annulated by the Pauson-Khand reaction. Several P.-K. conditions were explored and the best diastereoselectivity was observed when NMO was used as a promoter. The annulated product was isolated as an 11 1 mixture of diastereomers. 

The key bicyclo[4.3.0]nonenone intermediate in the total synthesis of ( )-13-deoxyserratine was prepared by a highly diastereoselective intramoiecuiar Pauson-Khand reaction of a functionalized enyne-cobalt complex in the laboratory... 

Verdaguer, X., Vazquez, J., Fuster, G., Bernardes-Genisson, V., Greene, A. E., Moyano, A., Pericas, M. A., Riera, A. Camphor-Derived, Chelating Auxiliaries for the Highly Diastereoselective Intermolecular Pauson-Khand Reaction Experimental and Computational Studies. J. 

This intramolecular Pauson-Khand reaction leading to spiro cyclopropane-l,2 -bicyclo[3.3.0]-octenones of type 30 is diastereoselective when the precursor 29 contains a chiral auxiliary on a carbonyl group adjacent to the triple bond or a stereogenic center on the three-membered... 

The use of chiral ligands has also been explored as a method of asymmetric induction in the Pauson-Khand reaction. To date, all of these reports have involved the addition of (P)-(-i-)-Glyphos to a preformed Co-alkyne complex and subsequent separation of the resulting diastereomers by HPLC. Under reaction conditions which prevented isomerization of the alkyne complex, the subsequent Pauson-Khand reaction proceeded with high levels of diastereoselectivity (Scheme 8)... 

This hetero-Pauson-Khand reaction is a complete diastereoselective synthesis of y-butyrolactones from the condensation of an alkene, a carbonyl moiety and CO. In a single process, two carbon-carbon bonds and two rings are constructed. The catalytic variant of this procedure has been also established on conjugated aromatic ketones (Scheme 12.44) [64]. 

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