Acetylide ions with aldehydes

Acetylenic alcohols result when acetylides add to ketones and aldehydes (Section 9-7B). Reaction of the acetylide ion with 2-methylpropanal gives one of the groups needed on the triple bond. 

You have already had considerable experience with caibanionic compounds and their- applications in synthetic organic chemistry. The first was acetylide ion in Chapter 9, followed in Chapter 14 by organometallic compounds—Grignaid reagents, for exanple—that act as sources of negatively polarized car bon. In Chapter 18 you learned that enolate ions—reactive intermediates generated from aldehydes and ketones—are nucleophilic, and that this property can be used to advantage as a method for carbon-carbon bond formation. 

Other carbanionic groups, such as acetylide ions, and ions derived from a-methylpyridines have also been used as nucleophiles. A particularly useful nucleophile is the methylsulfinyl carbanion (CH3SOCHJ), the conjugate base of DMSO, since the P-keto sulfoxide produced can easily be reduced to a methyl ketone (p. 549). The methylsulfonyl carbanion (CH3SO2CH2 ), the conjugate base of dimethyl sulfone, behaves similarly, and the product can be similarly reduced. Certain carboxylic esters, acyl halides, and DMF acylate 1,3-dithianes (see 10-10. )2008 Qxj(jatjye hydrolysis with NBS or NCS, a-keto aldehydes or a-... 

Li and coworkers have reported a novel silver-catalyzed, three-component coupling of an aldehyde, an amine, and an alkyne, and the first example of a direct addition of a silver acetylide to an aldehyde to produce propargylic alcohols (Scheme 1.41).103-105 Treatment of an aldehyde with a silver halide and secondary amine gave propargylic amines in good yields in organic solvent, water, or ionic liquids. The proposed mechanism suggests addition of a silver acetylide to the iminium ion formed in situ. 

Treatment of lithium acetylide with a primary alkyl halide (bromide or iodide) or with aldehydes or ketones produces the corresponding monosubstituted acetylenes or propargylic alcohols. Mercuric ion-catalyzed hydration of these furnishes methyl ketones and methyl a-hydroxy ketones, respectively. 

An acetylide ion is another example of a carbon nucleophile that reacts with an aldehyde or a ketone to form a nucleophilic addition product. When the reaction is over, a weak acid (one that will not react with the triple bond, such as the pyridinium ion shown here) is added to the reaction mixture to protonate the alkoxide ion. 

Given the structure or name of an aldehyde or ketone, write an equation for its reaction with the following nucleophiles alcohol, cyanide ion, Grignard reagent or acetylide, hydroxylamine, hydrazine, phenylhydrazine, 2,4-dinitrophenylhydrazine, primary amine, lithium aluminum hydride, and sodium borohydride. 

Acetylides are strong bases and are good nucleophiles. So they can add to the carbonyl groups in aldehydes and ketones. The alkoxide ion that is formed during the reaction can be protonated to an alcohol by treating it with aqueous dilute acid. 

---