Condensations carbonyls, sodium hydride

Reaction of a-sulphinyl carboxylic esters 421 with carbonyl compounds has usually been performed using a Grignard reagent as a base. No condensation products are obtained using f-butyllithium or sodium hydride - (equation 251). The condensation products formed are convenient starting materials for the synthesis of a, ) -unsaturated esters and j -ketones . ... 

Oxazolidinones are the products of the acid-catalyzed condensation of a-hydroxyamides with aldehydes and ketones (equation 178). Tertiary amides derived from pyruvic acid undergo intramolecular cyclization when irradiated (equation 179) (78JOC419). Treatment of the a-bromo amide (308) with sodium hydride yields inter alia the dimeric oxazolidinone (309), presumably by way of an a-lactam, which adds to the carbonyl group of a second molecule of the amide (equation 180) (80JCS(P1)2249). 

The illustrated product results from a dimerization of the starting material through a multistep process. As illustrated below, initial deprotonation of the starting material with sodium hydride generates an acyl anion that adds, through a 1,4-addition, to the carbonyl of a second starting material molecule. Subsequent proton transfer sets up the intermediate species for an aldol condensation. 

CHj)jC = C(COjC2Hs )CHjCOjCjH5 (41%). Cyclohexanone has been similarly condensed. Potassium t jutoxide and sodium hydride are excellent catalysts for condensations involving aryl ketones. Here, acid esters are formed which are readily decarbethoxylated to a tautomeric mixture of olefinic acid and lactone. The over-all process combined with reduction of the lactones or olefinic acids is a method of introduction of a propionic acid residue at the site of a carbonyl group of a ketone. 

More commonly, sodium hydride is used as a base for carbonyl condensation reactions. For exarrple, Claisen condensations of ethyl acetate and ethyl isovalerate are effected by sodium hydride. Condensations of cyclohexanone with methyl benzoate and ethyl formate (eq 16) are also facile. Sodium hydride can... 

Common bases used for this purpose are sodium alkoxides or sodium hydride. The ester enolate, once formed, can act as a carbon nucleophile and add to the carbonyl group of another ester molecule. This reaction is called the Claisen condensation. It is a way of making /3-keto esters. We will use ethyl acetate as an example to see how the reaction works. 

Lithium diisopropylamide sodium hydride Anion-anion condensation Poly-y -carbonyl compds. 

Semi-stabilized arsonium ylides react with lactones and thiolactones to give products of olefination. For example, the ylide from triphenylbenzylarsonium bromide and sodium hydride reacts with benzo-a-pyrone to give the benzylidene (35) as the exclusive product. Carbonyl-stabilized arsonium ylides fail to condense with benzo-a-pyrone. 

The dianiotf derived from a j3-ketoester by sequential treatment with sodium hydride and n-butyl-lithium alkylates exclusively at the y-position initial sodium enolate formation precludes the formation of carbonyl addition products and subsequent artifacts observed in the use of n-butyl-lithium alone. In addition to providing a convenient route to y-alkylated aceto-acetic esters, such dianions undergo ready aldol condensation, leading, after dehydration, to y3-unsaturated /3-ketoesters (Scheme 25). 

In the general context of donor/acceptor formulation, the carbonyl derivatives (especially ketones) are utilized as electron acceptors in a wide variety of reactions such as additions with Grignard reagents, alkyl metals, enolates (aldol condensation), hydroxide (Cannizzaro reaction), alkoxides (Meerwein-Pondorff-Verley reduction), thiolates, phenolates, etc. reduction to alcohols with lithium aluminum hydride, sodium borohydride, trialkyltin hydrides, etc. and cyloadditions with electron-rich olefins (Paterno-Buchi reaction), acetylenes, and dienes.46... 

An early approach to the synthesis of cephalotaxine (Scheme 32) was reported by Dolby et al. (64) in 1972, shortly before Auerbach s and Wein-reb s report (22). The Vilsmeier-Haack condensation of piperonylamide 187 with pyrrole yielded ketone 188, which was successively reduced with sodium borohydride, hydrogenated, and acylated to give the precursory chloro amide 189. The photocyclization of 189 produced lactam 190, which, after reduction of the carbonyl with lithium aluminum hydride and subsequent oxidation with mercuric acetate, yielded the enamine 43. This mate-... 

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