Acyl radical, synthon

The process can be interrupted at the stage of ketyl 171, thereby providing access to an acyl radical synthon. The radical character of the intermediate is... 

Table 8. Cyclization of carboxylic acids onto alkenes acyl radical synthon...

For the route A, acyl radicals donors like iS are readily generated from acyl selenides (ISa) or acyl cobalt derivatives (iSb) and radicals acceptors 2S are usually multiple bonds as in methyl vinyl ketone (2Sa) -although some homolytic substitutions are possible. On the other hand, nitriles GSal are useful acceptors (3S) in radical cyclisations and 4Sa is an obvious synthon equivalent of radical donor 4S (See Table 7.2). 

Note that aldehydes can also be a source of acyl radicals ( 0=0) via reaction with transition metal salts such as Mn(III) acetate or Fe(II) compounds.Another useful variation employs imidoyl radicals as synthons for unstable aryl radicals. 

Reduction of Thiol Esters with Sml2 and Synthetic Application as Synthons of Unstable Acyl Radicals... 

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. 

Very recently, Kim and co-workers have reported a new useful radical acylation approach which uses a series of sulfonyl oxime ethers, some of which function as a viable radical Cl synthon. Unlike carbon monoxide and isonitriles, which operate as a radical acceptor/radical precursor type Cl synthon, sulfonyl oxime ethers... 

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],... 

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