Carbon carbonylation with organoboranes

Reductive carbonylation and alkylation of imines.3 This cobalt carbonyl catalyzes a reaction of imines with organoboranes and carbon monoxide that results in amides. / -Keto amides are obtained from a-keto imines by this reaction. 

Stereochemistry. Brown4 has shown that the carbonylation reaction and the carboethoxymethylation reaction are highly stereospecific in that the original boron-carbon bond is converted into a carbon-carbon bond with retention of configuration. These reactions thus are similar to oxidation of organoboranes with alkaline hydrogen peroxide and animation with hydroxylamine-O-sulfonic acid. 

Reactions.—A variety of interesting and useful syntheses have been published involving the reaction of dimsyl anion [MeS(0)CHa ] with esters and lactones,with disulphides, with chlorosilanes, with sulphinate esters, with organoboranes, and with stilbenes. Simple and functionalized a-sulphinyl carbanions can be condensed with carbonyl compounds or alkylated, often in a stereocontrolled manner, as in a nicely conceived synthesis of biotin. Considerable attention has been given to methods for the removal of the sulphoxide function following carbon-carbon bond formation. Among the methods used are reduction by aluminium amalgam (with j3-keto-sulphoxides), reduction with Raney nickel, pyrolytic elimination of sulphenic acid, elimination of sulphur dioxide from sultines, e.g. (64), and sulphoxide-... 

Organoboranes can also be used to construct carbon-carbon bonds by several other types of reactions that involve migration of a boron substituent to carbon. One such reaction involves a-halo carbonyl compounds.20 For example, ethyl bromoac-etate reacts with trialkylboranes in the presence of base to give alkylated acetic acid derivatives in excellent yield. The reaction is most efficiently carried out with a 9-BBN derivative. These reactions can also be effected with (3-alkenyl derivatives of 9-BBN to give (3,y-unsaturated esters.21... 

The reaction of organoboranes with carbon-nitrogen multiple bonds always leads to aminoborane derivatives through a hard-hard interaction. Hydro-boration of nitriles with optically active diisopinocampheylborane (43) constitutes a key step in an asymmetric synthesis of amino acids (44). Carbonyl compounds are deoxygenated via hydroboration of their tosylhydrazones (45). 

Organoboranes can also be used to construct carbon-carbon bonds by two other types of reactions in which a migration of an alkyl group from boron to carbon is involved. Certain -unsaturated carbonyl compounds react with trialkyl-boranes with the net transformation being transfer of one alkyl group from the borane to the / -carbon atom of the unsaturated system. A free-radical mechanism... 

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