Cyclopentenones Wacker oxidation

The Wacker reaction provides a method for the preparation of 1,4-dicarbonyl compounds, by formation of an enolate, allylation with an allyl halide, followed by palladium-catalysed oxidation of the terminal alkene. The product 1,4-dicarbonyl compounds can be treated with base to promote intramolecular aldol reaction (Robinson annulation - see Section 1.1.2) to give cyclopentenones. Thus, in a synthesis of pentalenene, Wacker oxidation of the 2-aUyl ketone 115 gave the 1,4-diketone 116, which was converted to the cyclopentenone 117 (5.115). ... 

The cyclopentenone 19 can be prepared by an intramolecular aldol reaction from the diketone 18. This reaction is best achieved with a base such as KOH in MeOH and heat. The diketone 18 can be prepared by Wacker oxidation of the alkene 17. Standard conditions for the Wacker oxidation are 10 mol% PdCla, CuCl, O2, DMF, H2O (see Scheme 5.115). The alkene 17 is prepared by allylation of the enamine of cyclohexanone. See J. Tsuji, I. Shimizu and K. Yamamoto, Tetrahedron Lett. (1976), 2975. 

One such example is shown in Scheme 9, where intermediate 20 was swiftiy taken to 37 in a one-pot deprotection-tosylation-intramolecular y-alkylation mechanism utilizing tosyl fluoride. The resulting terminal olefin, when subject to Tsuji-Wacker oxidation conditions, furnished methyl ketone 38, which when exposed to strongly basic conditions triggered the Robinson annulation sequence, providing us with a cyclopentenone annulated analog 39. 

---