Alkyl sulfonates reduction

The Julia-Lythgoc olefination operates by addition of alkyl sulfone anions to carbonyl compounds and subsequent reductive deoxysulfonation (P. Kocienski, 1985). In comparison with the Wittig reaction, it has several advantages sulfones are often more readily available than phosphorus ylides, and it was often successful when the Wittig olefination failed. The elimination step yields exclusively or predominantly the more stable trans olefin stereoisomer. 

Sulfonic acids are prone to reduction with iodine [7553-56-2] in the presence of triphenylphosphine [603-35-0] to produce the corresponding iodides. This type of reduction is also facile with alkyl sulfonates (16). Aromatic sulfonic acids may also be reduced electrochemicaHy to give the parent arene. However, sulfonic acids, when reduced with iodine and phosphoms [7723-14-0] produce thiols (qv). Amination of sulfonates has also been reported, in which the carbon—sulfur bond is cleaved (17). Ortho-Hthiation of sulfonic acid lithium salts has proven to be a useful technique for organic syntheses, but has Httie commercial importance. Optically active sulfonates have been used in asymmetric syntheses to selectively O-alkylate alcohols and phenols, typically on a laboratory scale. Aromatic sulfonates are cleaved, ie, desulfonated, by uv radiation to give the parent aromatic compound and a coupling product of the aromatic compound, as shown, where Ar represents an aryl group (18). 

Beau and Sinay described a method which laid the groundwork for cyanohydrin acetonide alkylations [1]. Their strategy involved alkylation and reductive desulfonylation of glucopyranosyl sulfones 4. In this one-pot procedure, low temperature alkylation and subsequent reductive desulfonylation with lithium naphthalenide generated -C-glycosides with good selectivity >10 1 j3 a) and in moderate to good yield (Eq. 1). 

A further eight steps were required to convert the cyclopentanone 52 into the sulfone 59 that was deprotonated and treated with an allylic bromide (60) to afford the alkylated sulfone 61 (Scheme 7). The sulfone moiety and the benzyl ether protecting group were reductively removed in a one-pot procedure to afford a mono-protected diol (62). 

Another sulfone-based elimination of large applicability was proposed by Julia [418,419], Condensation of a metalled phenyl alkyl sulfone with a carbonyl compound, functionalization of the alkoxide and reductive elimination leads to an olefin. 

Trialkylaluminums, 21 By geminal alkylation of carbonyl groups Dichlorodimethyltitanium, 216 From reduction of alkyl halides, alkyl sulfonates and similar compounds From acetates or other esters Triphenylsilane, 334 From alcohols... 

Simple aliphatic sulfones, RS02R are polarographically inactive both in pro tic and aprotic media methylene disulfones are, however, reducible in DMF at potentials close to the decomposition potential of the medium. S-Disulfones and benzyl sulfones are rather acidic and may function as proton donors during the reduction, and their anions are generally not reducible [150]. Alkyl aryl sulfones and diaryl sulfones are reducible under protic and aprotic conditions [151-154] during the reduction of long chain aryl alkyl sulfones the EGB may induce a 6-cleavage, and in some cases dimerized products are observed [155]. The electrochemistry of sulfones has been reviewed by Chambers [103] and Simonet [156]. 

Desulfuration a-alkylation of -keto sulfones. Reductive alkylation of sul-fones is routinely carried out by a-alkylation of the enolate followed by desulfuration (Al/Hg). It can also be effected in one pot by desulfuration with lithium in liquid ammonia, which generates an enolate that can be alkylated. The yield is markedly enhanced by conversion of the lithium enolate to an alkylstannyl enolate by addition of BusSnCl with HMPT as cosolvent. 

Sulfones. Or react with sulfony 1 c Alkylations. involves reductive. ... 

Among the different methods for the formation of C-C double bonds, the reductive elimination of (3-functionalized (mainly P-hydroxy or (3-carboxy) sulfones, is one of the most widely used ones in organic synthesis. The reductive elimination of (3-hydroxy sulfones and derivatives is the so-called Julia,94 or Julia-Lythgoe olefination reaction (Eq. 2). It usually involves a condensation between the anion of an alkyl sulfone and a carbonyl compound to afford a (3-hydroxy sulfone (Eq. 47). The metal alkoxide intermediate is typically transformed in situ into a carboxylic or sulfonic ester derivative, which is then reduced... 

Use of Metals in Alcoholic Solvents. Magnesium in the presence of mercuric chloride as a catalyst is by far the most employed metal when the reductive desulfonylation is carried out in low molecular weight alcoholic solvents.112 Only a small number of examples exist where Na or Li in alcoholic solvents is used, mostly for the desulfonylation of alkyl sulfones. The use of Mg in a low molecular weight alcoholic solvent in the presence of mercuric chloride is an extremely convenient desulfonylation method for a wide variety of sulfones (Eq. 61).113 Although p-kctosul tones are inert towards this reagent,114 a-sulfonyl esters are efficiently desulfonylated by Mg in MeOH.115116... 

Tri-n-butyltin hydride is unproductive in the reduction of non-activated alkyl phenyl sulfones. Thus, the selective desulfonylation of a p-kcto phenyl sulfone in the presence of an alkyl sulfone is possible. Another interesting example of chemoselectivity is seen in the reduction of a-arylsulfonyl phosphonates.176 Tin hydride reduction of this kind of non-activated sulfone produces C-P fragmentation to afford the corresponding sulfone derivatives (Eq. 106a). In contrast, it... 

The second recent variant, developed by Julia and co-workers, avoids reductive elimination altogether and provides a remarkable one-pot connective synthesis of alkenes. The procedure, illustrated in eq 14, involves condensation of an aldehyde or ketone with a lithiated benzothiazolyl alkyl sulfone to give an adduct which first cyclizes and then fragments with extrusion of sulfur dioxide, benzothiazolone (which then tautomerizes to 2-hydroxybenzothiazole), and the alkene. Generally a mixture of ( )- and (2)-alkenes is obtained, hut in stericaUy hindered substrates the ( ) isomer can be obtained selectively. The same reaction has been observed with the pyridinyl sulfone analogs, in which case the separable /8-hydroxy sulfone intermediates undergo stereospecific and elimination to the corresponding alkene. 

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