Aryl sulfones, elimination

Different kinds of alkyl and aryl sulfonates 7 have been transformed to the fluorides 8 under fairly mild conditions with potassium fluoride in polyethylene glycol 400.145 No trace of elimination products, normally found due to attack of a second mole of potassium fluoride on the fluoroalkane eliminating hydrogen fluoride, is observed and the hydrolysis product is present only in 4% yield. No displacement of the tosylate group occurred for neopentyl tosylate. 

The saturated aqueous solution of surfactant at 25°C is in equilibrium with a liquid crystalline phase which contains about 25 wt% water. This phase dispersed in solution is the same as the phase formed by water vapor sorption into initially dry surfactant, according to nmr spectroscopy (which virtually eliminates the possibility, mentioned in the Introduction, of a complicating triple point in the two-component system). This hydrated liquid crystal is probably lamellar, to judge by the similarities in texture with lamellar liquid crystals of phospholipids and water (36). It is not uncommon for surfactants for form liquid crystalline phases by absorption of water, or hydrocarbon, or both (37). Moreover the true solubility of many other surfactants (particularly alkyl aryl sulfonates) in water, in salt water, and in hydrocarbon is small, sometimes as small as 0.003 wt% in water, below the Krafft point (38,39). Hence the present finding of liquid crystalline phase in equilibrium with isotropic aqueous solution at surfactant levels above 0.1 wt% may be representative of broad classes of surfactants, including some of interest in connection with... 

Alkyl radicals have been used to abstract hydrogen atom from C-H bonds at secondary carbon centers. For instance, Fuchs has developed a self-immolative elimination of aryl sulfones [84]. The or/Ao-silylated sulfone gives upon treatment with tin hydride and AIBN a primary alkyl radical that abstracts a hydrogen atom in a... 

Simpkins has presented an attractive method for the elimination of aryl sulfones [134]. >r// o-Bromophenyl sulfones gave alkenes via a 1,5-hydrogen transfer followed by fragmentation of a sulfonyl radical according to Scheme 38. The scope and... 

Synthesis of carotinoids via sulfones. FischU and Mayer have developed a synthesis of carotinoids based on the fact that allylic aryl sulfones in the presence of base readily eliminate arylsulfinic acid with formation of a conjugated double bond. An example is the synthesis of 15,15 -dehydro- 3-carotene... 

The aryl palladium complexes that are formed via oxidative coupling of aryl halides with palladium(O) can undergo the Heck reaction.238,239 -p e Heck reaction is the coupling of aryl halides or aryl sulfonate esters with alkenes.340 The reaction proceeds with formation of a palladium species such as 401, with elimination of palladium to give arylated alkene derivatives.241 Aryl halides differ greatly in their reactivity, Arl being the most reactive, followed by aryl bromides. In general, aryl chlorides are very unreactive in the Heck... 

Another basic difference between the two materials is that Oasis HLB is macroporous (80 A pores) while LiChrolut EN and Isolut ENV+ are basically nanoporous materials with the maximum pore size distribution located at 20—30 A. For this reason, the latter sorbents perform much better in extracting smaller molecules with molecular masses less than 500 Da, as is the case with the above halogenated acetic acid derivatives [326, 327] or aryl sulfonates [328]. On the contrary, macroporous Oasis HLB is the material of choice when larger analytes are the target of pre-concentration procedures, as was the case with tetracycline and macroHde antibiotics [321-324]. Another vivid example of this kind is pre-concentration of soy isoflavones [331], where Oasis HLB and macroporous Strata X display by far higher recovery values. On the other hand, the size exclusion effect can be exploited purposefully when only smaller molecules have to be retained with the elimination of the major sample matrix. The best example of this type of applications is the analysis of drugs and drug metaboHtes in whole blood or blood plasma [273-275]. Here the microporous hypercrosslinked polystyrene Purosep-270 is the best possible SPE material since it functions as an RAM. 

Introduction of arylsulfonylmethyl substituents into nitroheteroaromatic rings is of great practical value because these sulfones are versatile intermediates in organic synthesis. Nitrobenzyl aryl sulfones and their heterocyclic analogues can easily be transformed into the corresponding ethenyl derivatives by a simple alkylation with simultaneous elimination of arylsulfinate anion [125]. Diethyl methylenemalonate substituent can be introduced in the positimi 4- of 5-nitroimidazole via the VNS reaction of 5-nitroimidazole with the carbanion of chloromethyl phenyl sulfone [112, 124], followed by condensation of the obtained 4-(phenylsulfonyl)methyl derivative with diethyl bromomalonate or diethyl ketomalonate (Scheme 33) [126]. 

Carbanions of benzyl aryl sulfones are able to react with 2-nitrosodiphenylamines to produce 1,2-diaryIbenzimidazoles. The reaction appears to proceed via attack of these carbanions on the nitroso group followed by intramolecular addition-elimination process to give benzimidazoles (Scheme 1(X)) [83]. 

The three basic steps in the palladium-catalysed Suzuki-Miyaura reaction involve oxidative addition, transmetalation, and reductive elimination. A systematic study of the transmetalation step has found that the major process involves the reaction of a palladium hydroxo complex with boronic acid, path B in Scheme 3, rather than the reaction of a palladium halide complex with trihydroxyborate, path A. A kinetic study using electrochemical techniques of Suzuki—Miyaura reactions in DMF has also emphasized the important function of hydroxide ions. These ions favour reaction by forming the reactive palladium hydroxo complex and also by promoting reductive elimination. However, their role is a compromise as they disfavour reaction by forming of unreactive anionic trihydroxyborate. A method for coupling arylboronic acids with aryl sulfonates or halides has been developed using a nickel-naphthyl complex as a pre-catalyst. It works at room temperature in toluene solvent in the presence of water and potassium carbonate. ... 

The addition of alkyl radicals to vinyl sulfones to give functionalized alkenes via an addition-elimination sequence has been investigated by Russell and coworkers in some details [132, 147]. This reaction has recently been extended to unsaturated sulfimides, allowing the synthesis of styryl tetrahydrofurans and tetrahydropyrans [148]. The extension of this approach to phenylsulfonyl oxime ethers and heteroaromatic aryl sulfones (/p o-substitution) has recently been obtained with success [149, 150]. An example which comes from the work of Kim et al. is reported in equation (76) [149]. In this radical sequence, the alkyl radical generated photochemically from an alkyl iodide, in the presence of 1.2 equivalent of hexabutylditin, adds readily to the C=N bond of the oxime ether to... 

Three possible mechanisms may be envisioned for this reaction. The first two i.e. 1) Michael addition of R M to the acetylenic sulfone followed by a-elimination of LiOjSPh to yield a vinyl carbene which undergoes a 1,2 aryl shift and 2) carbometallation of the acetylenic sulfone by R M followed by a straightforward -elimination, where discarded by the authors. The third mechanism in which the organometallic reagent acts as an electron donor and the central intermediates is the radical anion ... 

Another general process involves the reaction of Pd(0) species with halides or sulfonates by oxidative addition, generating reactive intermediates having the organic group attached to Pd(II) by a ct bond. The oxidative addition reaction is very useful for aryl and alkenyl halides, but the products from saturated alkyl halides often decompose by (3-elimination. The a-bonded species formed by oxidative addition can react with alkenes and other unsaturated compounds to form new carbon-carbon bonds. The... 

There are a number of procedures for coupling of terminal alkynes with halides and sulfonates, a reaction that is known as the Sonogashira reaction.161 A combination of Pd(PPh3)4 and Cu(I) effects coupling of terminal alkynes with vinyl or aryl halides.162 The reaction can be carried out directly with the alkyne, using amines for deprotonation. The alkyne is presumably converted to the copper acetylide, and the halide reacts with Pd(0) by oxidative addition. Transfer of the acetylide group to Pd results in reductive elimination and formation of the observed product. 

Synthetically important substitutions of aromatic compounds can also be done by nucleophilic reagents. There are several general mechanism for substitution by nucleophiles. Unlike nucleophilic substitution at saturated carbon, aromatic nucleophilic substitution does not occur by a single-step mechanism. The broad mechanistic classes that can be recognized include addition-elimination, elimination-addition, and metal-catalyzed processes. (See Section 9.5 of Part A to review these mechanisms.) We first discuss diazonium ions, which can react by several mechanisms. Depending on the substitution pattern, aryl halides can react by either addition-elimination or elimination-addition. Aryl halides and sulfonates also react with nucleophiles by metal-catalyzed mechanisms and these are discussed in Section 11.3. 

---