Problem17.8 what reagent would would you use to accomplish each of the following reactions?
what carbonyl compounds give the following alcohols on reduction with LiAlH4?
17.6 Alcohols from Reaction of Carbonyl Compounds with Grignard reagents
we sew in section 10.8 that alkyl, aryl, and vinylic halides react with magnesium in ether or tetrahydrofuran solution to generate Grignard reagents, RMgX.These Grignard reagents react with carbonyl compounds to yield alcohols in much the same way that hydride reducing agents do. The result is a useful and general method of alcohol synthesis
A great many alcohols can be obtained from Grignard reactions, depending on the reactants.For example, Grignard reagents react with formaldehyde
H2C=O, to give primary alcohols, with aldehydes to give secondary alcohols, and with ketones to give tertiary alcohols:
Esters react with Grignard reagents to yield tertiary alcohols in which two of the substituents bonded to the hydroxyl-bearing carbon have come from the Grignard reagent (just as LiAlH4 reduction of an ester adds two hydrogens)
Carboxylic acids don't give addition products with Grignard reagents because the acidic carboxyl hydrogen reacts with the basic Grignard reagent to yield a hydrocarbon and the magnesium salt of the acid. we saw this reaction in section 10.8 as a means of reducing alkyl halides to alkanes.