Oxidative desulfonylation

Oxidative desulfonylation polyenes. Oxidation of the anion of a primary sulfone with MoOPH results in a p-hydroxy sulfone formed by condensation of... 

AUtyl, allyl, benzyl and cycloalkyl sulfones can be converted to aldehydes or ketones in good to excellent yields by treatment with n-BuLi followed by BTSP. Carbonyl-O labeling was achieved in situ by using oxidative desulfonylation with (Me3Si)2 02 (equation 50) . 

Oxidative desulfonylation.- Aryl sulfones are converted into ketones by oxidation of the a-carbanion (LDA) with Mo05Py-HMPT in THF at —78 in 50-97% yield. This conversion permits use of phenyl vinyl sulfone as an equivalent of kctcnc in Diels Alder reactions. 

Oxidative desulfonylation Chlorodimethoxyborane, 73 Oxidative hydrolysis see Hydrolysis) Oxy-Cope rearrangement see Sigma-tropic rearrangements) Oxymercuration see Addition reactions to carbon-carbon multiple bonds)... 

Oxidative desulfonylation. The a-anion of alkyl phenyl sulfones on reaction with 1 is converted into aldehydes or ketones in good to high yield (equation I). 

Oxidative desulfonylation of p-acetoxy or p-tetrahydropyranyloxy sulfones provides a novel route to diynes, enynes, and polyenes. 

The sulfone is a versatile functional group comparable to the carbonyl functionality in its ability to activate molecules for further bond construction, the main difference between these two groups being that the sulfone is usually removed once the synthetic objective is achieved. The removal most commonly involves a reductive desulfonylation process with either replacement of the sulfone by hydrogen (Eq. 1), or a process that results in the formation of a carbon-carbon multiple bond when a P-functionalized sulfone, for example a (3-hydroxy or (3-alkoxy sulfone, is employed (Eq. 2). These types of reactions are the Julia-Lythgoe or Julia-Paris-Kocienski olefination processes. Alkylative desulfonylation (substitution of the sulfone by an alkyl group, Eq. 3), oxidative desulfonylation (Eq. 4), and substitution of the sulfone by a nucleophile (nucleophilic displacement, Eq. 5) are also known. Finally, p-eliminations (Eq. 6) or sulfur dioxide extrusion processes (Eqs. 7, 8 and 9) have become very popular for the... 

Compound 12 was first subjected to the Hosomi-Sakurai reaction [6] to give 17, which was converted to 18 via m-chloroperbenzoic acid (MCPBA) oxidation etc. [7a, b]. The lithium salt of 19, derived from 1-0-benzylbutane-1,2(1 ), 4-triol, was added to 18 in tetrahydrofuran to give the adduct. Oxidation, desulfonylation, and removal of the benzylidene and ethoxyethyl groups gave the triol (20), which was readily converted to the aldehyde (segment B 16) [7b]. 

One of the most prominent characteristics of Fe(+2) is its ability to undergo oxidation leading to Fe(+3). This was used by Uchiyama et al. when they reported on Fe(+2)-ate complexes as potent electron transfer catalysts [7, 8]. These ferrates are accessible from FeCl2 and 3 equiv. of MeLi. The Fe(+2/+3) oxidation potential of [Me3Fe(+2)]Li 19 in THF is —2.50 V, thus being in between those of Sml2 (—2.33 V) and Mg (—3.05 V). With these alkyliron-ate complexes it was possible to realize a reductive desulfonylation of various A -sulfonylated amines 20 with different basicity. By using Mg metal to restore the active Fe(+2) species 19 a catalytic reductive desulfonylation process was achieved (Scheme 4). 

Structure, acidity and basicity 100 Oxidation of sulfinic acids 101 Disproportionation 102 Reactions with alkyl sulfides and disulfides 103 Desulfonylation 106... 

Dess-Martin Oxidation, 53, 1 Desulfonylation reactions, 72, 2 Desulfurization ... 

Methylation of free hydroxyl groups by means of Purdie s reagents usually proceeds smoothly,176 without occurrence of desulfonylation.220 Thus, by treatment20 of methyl 2,3-di-0-methyl-4-0-phenylsulfonyl-/8-D-glucoside with silver oxide plus boiling methyl iodide under reflux, the 2,3,6-trimethyl ether was obtained. However, although methyl... 

Diels-Alder reactions with unreactive alkenes. The adducts of 1 with alkcnes are oxidized by HjO, to vinylsulfones, which are usually satisfactory dienophiles. After the cycloaddition desulfonylation can be effected with zinc in HOAc. The sequence can be used to effect cycloadditions of unreactive alkenes. 

A procedure, devised by Kuhn and coworkers, that employs methyl iodide and silver oxide in N,N-dimethylformamide is frequently used for the permethylation of carbohydrates. When applied to sulfonic esters of carbohydrates, two side-reactions are found if appropriate structures are present, namely 3,6-anhydro ring formation, and conversion of a primary methylsulfonyloxy group into a methoxyl group. These side reactions were minimized by conducting the meth-ylation at 0° instead of at room temperature, and by processing the reaction mixture as soon as the reaction was complete, as shown by thin-layer chromatography. With methyl 2,3-di-0-p-tolylsulfonyl-6-O-trityl-a-D-glucopyranoside, methylation was effected in 86% yield with methyl iodide and silver oxide in hot acetone, without occurrence of desulfonylation. 

Numerous aryl bromides, iodides [203], borates [204] and triflates [205, 206] have been successfully carbonylated. Triflates could serve as a route for the synthesis of arenecarboxylic acid derivatives from phenols. This carbonylation using dppf in a catalytic mixture generally shows higher efficiency than PPhj or P(o-Tol)3 [207]. Poor performance is also noted for PPhj in a Pd-catalyzed vinyl substitution of aryl bromides [208]. Side-reactions involving the formation of [PPhjAr]Br and ArH are responsible. A system which is catalyzed effectively by PdCljfdppf) under 10 atm CO is the desulfonylation of 1-naphthalenesulfonyl chloride 58 in the presence of Ti(OiPr)4. Formation of isopropyl 1-naphthoate 59 can be explained in a sequence of oxidative addition, SOj extrusion, carbonylation and reductive elimination (Fig. 1-27) [209]. A notable side-product is di-l-naphthyl disulfide. 

Similarly, ketone ( )-376 obtained by dihydroxylation of 366, followed by diol protection as acetonide, desulfonylation with Na/Hg, and Swem oxidation has been resolved by the Alex-... 

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