Sulfonyl oxime ethers

Radical chemistry has witnessed remarkable progress since the mid 1980s [1], In addition to common radical C2 synthons such as alkenes and alkynes [2], several radical Cl synthons are also available, including carbon monoxide, isonitriles, and sulfonyl oxime ethers [3, 4]. As featured in Scheme 6.1, a variety of combinations of radical Cl and C2 synthons are now possible, which makes radical methodologies more attractive and permits the design and implementation of a wide range of multicomponent processes. 

Radical C1 synthons CO, isonitrile, sulfonyl oxime ether, etc. Scheme 6.1... 

Sulfonyl oxime ethers function as efficient radical Cl acceptors [45]. The instance in Scheme 6.26, in which a bissulfonyl oxime ether is used as a radical Cl acceptor, showcases the strategic aspect of this unique method for the synthesis of... 

The combination of carbon monoxide with sulfonyl oxime ethers allow for a set of multicomponent coupling reactions involving consecutive Cl/Cl-type coupling, a rare class of radical multicomponent reactions. In Scheme 6.27, examples of three-, four-, and five-component coupling reactions are shown [46], In these reactions, allyltin is not incorporated into the product, but serves as an acceptor of the phenylsulfonyl radical and a source of the tributyltin radical, which delivers the radical chain. 

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. 

Radical Formylation of RX with a Sulfonyl Oxime Ether... 

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... 

It is noteworthy that this Cl reagent can be applied to a wide range of organic radicals involving rather stable radicals such as a-keto radical, a-alkoxyalkyl radical, and the benzyl radical for which the aforementioned radical formylation system with CO cannot be applied. The high reactivity of phenyl sulfonyl oxime ether is supported by kinetic studies [29]. The approximate rate constants for the addition of a primary alkyl radical to this phenyloxime ether was determined to be k=9.6xl0 M s at 25 °C, which is 1.8 times faster than the addition to aery-... 

A similar method for cyclic ketone synthesis via an intramolecular carbonyl ad-dition/elimination strategy has been reported by Kim and Jon, who used acylsul-fides and acylselenides as radical acceptors (Scheme 4-21) [41]. As has previously been observed in the cases of sulfonyl oxime ethers which liberate sulfonyl radicals, thiyl and selenenyl radicals react with ditin to propagate the chain. Generally acylselenides are more efficient substrates than acylsulfides due to the better leaving ability of the phenylseleno group. As shown in the third example in Scheme 4-21, a tandem cyclization leading to a tricyclic ketone has also been effected. 

Radical Acylation with Sulfonyl Oxime Ethers... 

Radical carbonylation of an alkyl iodide in the presence of Kim s sulfonyl oxime ethers provides a new type of multi-component coupling reaction, and a typical example is given in Scheme 4-38 [65]. In this method, plural radical Cl synthons are consecutively combined. 

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],... 

Increasing interest is expressed in diastereoselective addition of organometallic reagents to the ON bond of chiral imines or their derivatives, as well as chiral catalyst-facilitated enantioselective addition of nucleophiles to pro-chiral imines.98 The imines frequently selected for investigation include N-masked imines such as oxime ethers, sulfenimines, and /V-trimcthylsilylimines (150-153). A variety of chiral modifiers, including chiral boron compounds, chiral diols, chiral hydroxy acids, A-sull onyl amino acids, and /V-sulfonyl amido alcohols 141-149, have been evaluated for their efficiency in enantioselective allylboration reactions.680... 

Few totally new syntheses have been reported. Autoclaving (165°C, 6 hr) of the sulfonyl chloride 40 with sulfur and ammonia gives60 a moderate yield of saccharin (41). Photolysis of the oxime ether 42 affords N-alkoxysaccharins... 

The reaction between sulfonyl chlorides and cycloalkanone oximes in the presence of pyridine is followed by Beckmann rearrangement to the imidochlorides, which give the corresponding lactim ethers with alcohol.58... 

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