Enolate anions, nitro compounds, reaction with aldehydes

Aliphatic nitro compounds show a number of reactions which parallel those of carbonyl chemistry. Primary and secondary nitro compounds exhibit tautomerism paralleling keto-enol tautomerism (Scheme 3.94a). Aliphatic nitro compounds dissolve in aqueous sodium hydroxide with the formation of sodium salts. The resultant anions behave as carban-ions and will condense with aldehydes. An example involves the formation of m-nitrostyrene from nitromethane and benzaldehyde (Scheme 3.94b). 

A new synthesis of aldehydes with 2-methyl-2-thiazoline has the advantage of releasing the aldehydes from the thiazolidine intermediate under neutral conditions . Acetylene derivatives can be obtained from aldehydes via dibromomethylene compounds Novel reactions of alkynes with cationoid electrophiles have been published. -Diketones and 2-ketoalkoximes can be obtained by this reaction from acid chlorides and aliphatic nitro compounds respectively Addition of aldehydes to activated carbon-carbon double bonds occurs smoothly in the presence of cyanide ions as catalysts . Poly- -carbonyl compounds have been prepared by condensation of two anions, whereby the enolate salt of a y8-keto ester condenses as an electrophilic anion with strong nucleophiles such as the dianion of benzoylacetone. ... 

Selenenyl halides are relatively stable, though moisture sensitive, compounds that are generally prepared by the reactions shown in Scheme 7 and behave as electrophilic selenium species. They react with ketones and aldehydes via their enols or enolates to afford a-seleno derivatives (e.g. (17) in equation 11). Similar a-selenenylations of /3-dicarbonyl compounds, esters, and lactones can be performed, although the latter two types of compounds require prior formation of their enolates. Moreover, the a-selenenylation of anions stabilized by nitrile, nitro, sulfone, or various types of phosphorus substituents has also been reported (equation 12). In many such cases, the selenenylation step is followed by oxidation to the selenoxide and spontaneous syn elimination to provide a convenient method for the preparation of the corresponding Q ,/3-unsaturated compound (e.g. 18 in equation 11). Enones react with benzeneselenenyl chloride (PhSeCl) and pyridine to afford a-phenylselenoenones (equation 13). 

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