Aldol condensation acetoxy group

Comforth has reviewed literature reports and independently studied the special cases of reaction of 1 with salicylaldehyde and with 2-acetoxybenzaldehyde. Coumarins (10) are afforded in the condensation of 1 with salicylaldehyde or its imine, whereas when 2-acetoxybenzaldehyde is used, acetoxy oxazolone 12 is the major product. The initial aldol condensation product between the oxazolone and 2-acetoxybenzaldehyde is the 4-(a-hydroxybenzyl)oxazolone 11, in which base-catalyzed intramolecular transacetylation is envisioned. The product 9 (R = Ac) can either be acetylated on the phenolic hydroxy group, before or after loss of acetic acid, to yield the oxazolone 12, or it can rearrange, by a second intramolecular process catalyzed by base and acid, to the hydrocoumarin, which loses acetic acid to yield 10. When salicylaldehyde is the starting material, aldol intermediate 9 (R = H) can rearrange directly to a hydrocoumarin. Comforth also accessed pure 4-(2 -hydroxyphenylmethylene)-2-phenyloxazol-5(4//)-one (13) through hydrolysis of 12 with 88% sulfuric acid. 

After Michael addition of 17 to 2-methyl-1,3-cyclohexanedione (19) and the first aldol condensation, the double bond in 20 is reduced to give 21. The acetoxy group in 21 is unmasked by hydrolysis and oxidation, and subsequent aldol condensation gives 22. Again, the terminal double bond in 22 is oxidized with PdCk to methyl ketone, and subsequent hydrogenation of the internal double bond affords the trione 23, from which the steroid A-ring 24 is formed by aldol condensation [34],... 

When 2-acetoxy-2-methylcyclopropyl hexyl ketone (11) was treated with sodium hydroxide in methanol, the cyclopentenone derivative dihydrojasmone (12) was obtained in good yield. It is assumed that the acetoxy group was hydrolyzed prior to the base-catalyzed cleavage reaction of the cyclopropanol derivative. Formation of the final product can be rationalized by an intramolecular aldol-type condensation. 

The synthesis involved formation of the (3-lactam 159 which was converted into its enolate and subjected to direct aldol condensation with excess of acetaldehyde to give 160 as a mixture of diastereomers in 80.9% yield. Further elaboration of the styryl group by known procedures afforded the ( )-4-acetoxy-(3-lactam 161 as intermediate of the 6P-methylcarbapenem derivative 162. 

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