Organometallic reagents reactions with carbon dioxide

Because organometallic reagents are strong nucleophiles, they react with many other electrophiles in addition to carbonyl groups. Because these reactions always lead to the formation of new carbon-carbon bonds, they are also valuable in organic synthesis. In Section 20.14, we examine the reactions of organometallic reagents with carbon dioxide and epoxides. 

We already know a number of routes to carboxylic acids, and this section will add an important new one, the reaction of organometallic reagents with carbon dioxide. 

Carboxylic acid groups can also be installed in molecules using the reaction of an organometallic compound with carbon dioxide. This is a reductive method since the carbon dioxide is reduced to a carboxylic acid by formation of a new carbon-carbon bond. Both Grignard reagents and organolithium compounds work well in this reaction. 

This is an excellent reaction for the conversion of most halides to acids containing one additional carbon atom. Carbonation of Grignard reagents and organoalkali compounds gives acids in yields of 50-85%. Ether solutions of the organometallic compounds formerly were treated with carbon dioxide gas at 10° to -10°. A more recent technique involves pouring the solution onto excess crushed Dry Ice. Carbon dioxide... 

The use of thienyl Grignard reagents, and more recently lithiated thiophenes, has been extensive and can be illustrated by citing formation of oxythiophenes, either by reaction of the former with f-butyl perbenzoate or the latter directly with bis(trimethylsilyl) peroxide or via the boronic acid, the synthesis of thiophene carboxylic acids by reaction of the organometallic with carbon dioxide, the synthesis of ketones, by reaction with a nitrile, or alcohols by reaction with aldehydes, by the reaction of 2-lithiothiophene with A -tosylaziridine, and by syntheses of thieno[3,2- ]thiophene and of dithieno[3,2- 2, 3 - /]thiophene. Some of these are illustrated below. 

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