Ketals 3-Keto acids, decarboxylation

Hydrogenation was carried out at O to minimize decarboxylation of the saturated 3-keto acid product 18. Mannich reaction proceeded with in situ decarboxylation to afford a-methylene ketone 19, which on Michael reaction with ketal 3 keto ester 20 -" yielded adduct 21. Saponification, B ring closure, and decarboxylation then led to ketalenone 23 in high yield, which was converted into ( + )-19-nortestosterone 24 and thence to ( + )-19-norandrostenedione 25 in 50% yield from 18 or 27% overall yield from 12. However, ketal hydrolysis, A ring closure, oxidation at C-17, and isomerization by the Roussel procedure (acetyl bromide-acetic anhydride in methylene chloride at 20°) should yield (-f )-estrone 26 efficiently. 

Ketones from y -ketocarboxylic acid esters with protection of the keto group as cyclic ketal Decarboxylation with cleavage of ketals... 

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