Claisen condensation 1,3-dicarbonyls from

The 1,3-dicarbonyl components can be replaced by an enol ether, which can be prepared by Claisen condensation from an ortho ester and a reactive methylene compound. ... 

The Claisen condensation is one method of synthesizing (3-dicarbonyl compounds, specifically a (3-keto ester. This reaction begins with an ester and occurs in two steps. In the first step, a strong base, such as sodium ethoxide, removes a hydrogen ion from the carbon atom adjacent to the carbonyl group in the ester. (Resonance stabilizes the anion formed from the ester.) The anion can then attack a second molecule of the ester, which begins a series of mechanistic steps until the anion of the (3-dicarbonyl compound forms, which, in the second reaction step (acidification), gives the product. 

The conversion of the substituted 1,3-dicarbonyl compound into homophthalic acid is remarkably facile loss of the acetyl group by a retro-Claisen condensation and hydrolysis of the ester group are complete in a few minutes in aqueous sodium hydroxide. The overall synthesis of homophthalic acids from o-bromobenzoic acids occurs in high yield and provides an attractive route. 

In 1967 Shimizu, Sakamoto and Fukushima [13] prepared 2-methyl-4-oxopyrano[2,3-b]pyridine (XIX, R = Me, R = R = H) in 27 per cent yield by condensing ethyl 2-methoxynicotinate with acetone followed by ring closure by heating under reflux with hydroiodic acid. When benzal-dehyde was used instead of acetone, 4-oxo-2-styryl[2,3-b]pyridine (XIX, R = CH CHPh, R = H) was obtained. Spectroscopic data (u.v., i.r. and n.m.r.) are also given for the products [13]. In the same year, Bonsall and Hill [14] reported a number of derivatives of (XIX, R = Me, Ph, C02Et, or CO2H R = R = Me) which they had prepared by the usual Claisen condensation of 3-acetyl-4,6-dimethylpyridine-2-one with appropriate dicarbonyl compounds followed by acid-cyclisations. Overall yields for these compounds were above 30 per cent. Sliwa [15] recently reported the synthesis of (XIX, R = Ph, R = R = H) from ethyl 2-ethoxy-nicotinate. 

The five-membered ring pyrazoles are even simpler as the starting material is a 1,3-dicarbonyl compound available from the aldol or Claisen ester condensations. 

The Reformatsky -Claisen variant is complicated by various side reactions, e.g., the condensation of the zinc enolate derived from acetic esters to yield 1,3-dicarbonyl compounds, known byproducts in the classical Reformatsky reaction. This side reaction is depressed by a-alkyl substitution of the ester. 

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