Carbon monoxide carbonyl synthon

Up until the end of the 1980s, radical carbonylation chemistry was rarely considered to be a viable synthetic method for the preparation of carbonyl compounds. In recent years, however, a dramatic change has occurred in this picture [3]. Nowadays, carbon monoxide has gained widespread acceptance in free radical chemistry as a valuable Cl synthon [4]. Indeed, many radical methods can allow for the incorporation of carbon monoxide directly into the carbonyl portion of aldehydes, ketones, esters, amides, etc. Radical carboxylation chemistry which relies on iodine atom transfer carbonylation is an even more recent development. In terms of indirect methods, the recent emergence of a series of sulfonyl oxime ethers has provided a new and powerful radical acylation methodology and clearly demonstrates the ongoing vitality of modem free radical methods for the synthesis of carbonyl compounds. 

The radical carbonylation of an alkyl iodide in the presence of Kim s sulfonyl oxime ethers [58, 59, 60] provides a new type of multicomponent coupling reaction where plural radical Cl synthons are consecutively combined [61]. In the transformation, allyltin was used to serve as a trap of benzenesulfonyl radical which converts sulfonyl radical to a tin radical, thus creating a chain. Scheme 14 illustrates such an example, where the product was easily dehydroxylated to give the corresponding tricarbonyl compound on treatment with zinc/AcOH. The radical acylation reaction by Kim s sulfonyl oxime ethers can be conducted under irradiation with the addition of hexamethylditin. This is an alternative path for achieving a similar transformation without the use of photolysis equipment. Scheme 15 illustrates several examples where carbon monoxide and Kim s sulfonyl oxime ethers are successfully combined to create new tandem radical reaction sequences [61],... 

---