p-Toluenesulfonic acid → Methyl 6,6-dimethoxyhexanoate

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Reaction Steps

56 g (0.4 Mole) of cyclohexanone enolacetate in 500 ml of methanol was ozonised in a dry ice-acetone bath until the solution turned blue. 60 ml of dimethyl sulphide was added, and the cooling bath was removed. The temperature rose slowly to 48°, and after it had returned to room temperature, 40 ml of trimethyl orthoformate and 1 ml of acetyl chloride were added. The mixture was then left for 48 h at room temperature. Three identical batches were combined and the solvent was removed in vacuo. The residue was dissolved in ether, washed with brine containing a small amount of NaHCO3, dried (Na2SO4), and distilled to give 193 g of product, b.p. 56°-69°/0.1 Torr. The NMR spectrum indicated the presence of ca. 20% of methyl 6-oxohexanoate. The product was mixed with 100 ml of trimethyl orthoformate, 20 ml of methanol, and 0.5 g of p-toluene sulfonic acid. The mixture was left for 48 h at room temperature, then worked up as above yielding 201 g (88%) of methyl 6,6-dimethoxyhexanoate. b.p. 61°/0.1 Torr.

Provenance & Evidence