Synthesis of 2-Alkyl-2-cyclopenten-1-ones. A Versatile Kinetic Alkylation-Ozonolysis Procedure for the Preparation of γ-Ketoaldehydes

A versatile kinetic alkylation-ozonolysis route for the synthesis of lactones: chiral γ-lactones and racemic δ-lactones

“…Water (20ml) was added and the mixture was extracted with ether (3x50ml). The combined ether layers were dried over MgSO 4 and, after removal of the solvent, the residue was kugelrohr distilled to give 6-hepten-2-one 5 (1.19g, 79%, 93% pure by GC) as a colourless liquid with a fruity smell whose spectroscopic data were in agreement with published data 37 .…”

“…The commercial availability and low cost of the starting material 6-methyl-5-hepten-2-one 1 is a key element in the attractiveness of the kinetic alkylation-ozonolysis route for the synthesis of γ-substituted-γ-lactones 5 and 2-alkylcyclopent-2-enones 4 . The availability of a suitable δ,ε-unsaturated ketone such as 6-hepten-2-one 5 is a prerequisite in the extension of this kinetic alkylation-ozonolysis approach to the synthesis of δ-substituted-δ-lactones.…”

“…Treatment of this mixture, or the pure δ-hydroxyester, with p-toluenesulfonic acid in refluxing benzene gives the δ-lactone 9 (Table 4). Despite the fact that the conversion of the δ-ketoesters 7 to the δ-lactones 9 proceeds in some cases in modest yields, this kinetic alkylation-ozonolysis based approach to the synthesis of δ-substituted-δ-lactones is competitive with most of those currently available in the literature, and the fact the method can also be applied to the preparation of chiral and racemic γ-substituted γ-lactones 5 and 2-substituted 2-cyclopenten-2-ones 4 , emphasizes the synthetic utility of this combination of reactions. Yield and purity of product after chromatography.…”

“…After removal of the solvent the residue was dissolved in dry benzene (20ml) containing p-toluenesulfonic acid (0.1g) and the solution was refluxed for 24h. Ether (50ml) was added, the solution was washed with brine (30ml) and 10% NaHCO 3 (30ml), and was dried over MgSO 4 . Following removal of the solvent the crude product was chromatographed on silica (petroleum ether/ether, 95:5) to give the γ-lactones (dihydro-5-alkyl-2(3H)-furanones) 4 as colourless liquids whose spectroscopic data were in agreement with literature data.…”

“…Many of these methods suffer from the disadvantages discussed above in relation to the synthesis of lactones. We have developed a versatile procedure (Scheme 1) which can be adapted to the synthesis of all these materials and have previously reported on its application to the synthesis of 2-alkyl-2-cyclopenten-1-ones 4 and racemic γ-substituted γ-lactones 5 . We now report on its use for the synthesis of chiral γ-substituted γ-lactones and racemic δ-substituted δ-lactones.…”