Sulfonyl-Stabilized Anions

Denmark has developed the carbanion accelerated Claisen rearrangement [15, 72-78]. It is known that the nature of the transition state of Claisen rearrangement is dependent on the substituents present [79]. The effects of substituents have been studied in detail by Carpenter [80]. At positions Cl, C2, and C4 both donor and acceptor substituents accelerate the reaction with respect to hydrogen (Eq. 3.1.58). Furthermore, the synthetic versatility of the Claisen rearrangement primarily resides in the variety of the substituents X that determine the carbonyl derivative 

Unsubstituted 104 and the tautomeric sulfone 105 reacted with potassium hydride and the crown ether in HMPA/THF to afford the rearrangement product 106 in 78% and 76% yield, respectively (Eq. 3.1.59). The position of the double bond had no effect on the yield or regiochemical outcome of the reaction. Substrates disubstituted at Cl rearranged much faster than the unsubstituted 104 (Eq. 3.1.60). It is expected that the anionic charge should not only provide accelerating potential but should also contribute to the exothermicity of the reaction. The 

When the allyl vinyl ether has at least a substituent at terminal allyl moiety, the addition of liCl improves the yield of rearrangement products (Eq. 3.1.61). 

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Cleavage of the hetero ring of 3-nitrobenzo[A]thiophene is the first step in a synthesis of ( )-2-aryl-l-[2-(methylsul-fonyl)phenyl]-l-nitroethenes (Scheme 176). The sulfonyl-stabilized anion derived from these alkenes by metallation adds in Michael fashion to the nitrovinyl unit to form 4-nitrothiochroman 1,1-dioxides as an inseparable mixture of two diastereomers. The overall process corresponds to expansion of a thiophene ring to a thiopyran unit <2004T4967>. 

Marshall and Cleary [115] synthesized 7 (8)-desoxyasperdiol 198), a precursor of the cembranoid asperdiol by using sulfonyl stabilized anion displacement of... 

In its original form,94 the Julia reaction consisted of the formation of a carbon-carbon double bond through the coupling of a sulfonyl-stabilized anion and a carbonyl compound to generate a P-hydroxy sulfone, followed by a reductive elimination to afford the alkene (Eq. 47). A subsequent study of its scope and stereochemistry led to improved reaction conditions, which are now widely used.206 Alternative methods to synthesize the P-hydroxy sulfone intermediates, such as the addition of sulfonyl carbanions to esters with subsequent reduction of the ketone to the P-hydroxy sulfone, are also known (Eq. 121).207... 

Phosphorus is like sulfur in this regard you can compare the phosphonium ylid with the sulfonyl-stabilized anions you met earlier. 

The alkylation of sulfur-stabilized anions has been the subject of an excellent recent review633. Anions adjacent to a wide range of sulfur functionalities may be alkylated readily, the most common being sulfoxide and sulfone a-anions. In the synthesis of retinoic acid derivatives and vitamin A634-636, a-sulfonyl anions have been alkylated with an co-acetoxy-containing allyl halide in good yield (equation 96). 

So far the reactivity of epoxides has involved their use as an electrophile. However, oxtranyl anions can serve as functionalized nucleophiles in their own right. Thus, the sulfonyl substituted epoxide 107 can be deprotonated with -butyllithium to provide a stabilized anion which engages in facile Sn2 reaction with triflate 108 <03JOC9050>. Other examples of such stabilized epoxide anions include those derived from oxazolinyloxiranes (e.g., 110), which react with nitrones to provide the spirotricyclic heterocycles of type 112, Hydrolysis provides the epoxy amino acids 113, in which the carboxylic acid moiety was provided by the oxazoline nucleus and the amine functionality was derived from the nitrone <03OL2723>. A recent report has demonstrated that oxiranyl anions can also be stabilized by the amide functionality <03H(59)137>. 

The anions of malonate esters, cyclopentadiene, p-keto esters, ketones, aldehydes, a-nitroacetate esters, Meldrum s acid, diethylaminophosphonate Schiff bases, p-diketones, /3-sulfonyl ketones and esters, andpolyketides represent the wide variety of carbon nucleophiles effective in this reaction. Generation of the stabilized anions normally is... 

Ab initio calculations and NMR spectroscopy have been used to probe the structure, aggregation, and reactions of sulfonyl-stabilized allylic norbomenyl and norbornyl carbanions. This has included characterization of the exo direction pyramidalized anionic carbon atoms. Lithiosulfones (10) and (11), which exist in THF at —108.5 °C as an approximately 1 1 mixture of monomeric and dimeric forms, have been found to equilibrate rapidly with the respective conjugate acids, (12) and (13), in both exo and endo forms at 100 °C. According to Li H - and H H -NOE experiments, the monomeric and dimeric species endo-(10) and endo- ll), having endo anions, seem to be preferred in THF solution. Ab initio calculations indicate that the C(2) atoms of endo-(10)(Li+) and endo-(ll)(Li+) are pyramidalized in the exo direction whereas the... 

The oxidative dimerization of the anion of methyl phenyl sulfone (from a Grignard reagent) in ethereal solution in the presence of cupric chloride in 5% yield has been reported47. Despite the reported48 poor stability of the a-sulfonyl C-centered radicals, Julia and coworkers49 provoked the dimerization (in 13 to 56% yields) of the lithiated carbanion of alkyl phenyl sulfones using cupric salts as oxidants. The best results are obtained with cupric triflates in THF-isobutyronitrile medium (56% yield for R = H). For allyl phenyl sulfones the coupling in the 3-3 mode is predominant. 

Ionic liquids are a class of solvents and they are the subject of keen research interest in chemistry (Freemantle, 1998). Hydrophobic ionic liquids with low melting points (from -30°C to ambient temperature) have been synthesized and investigated, based on 1,3-dialkyl imidazolium cations and hydrophobic anions. Other imidazolium molten salts with hydrophilic anions and thus water-soluble are also of interest. NMR and elemental analysis have characterized the molten salts. Their density, melting point, viscosity, conductivity, refractive index, electrochemical window, thermal stability, and miscibility with water and organic solvents were determined. The influence of the alkyl substituents in 1,2, 3, and 4(5)-positions on the imidazolium cation on these properties has been scrutinized. Viscosities as low as 35 cP (for l-ethyl-3-methylimi-dazolium bis((trifluoromethyl)sulfonyl)amide (bis(triflyl)amide) and trifluoroacetate) and conductivities as high as 9.6 mS/cm were obtained. Photophysical probe studies were carried out to establish more precisely the solvent properties of l-ethyl-3-methyl-imidazolium bis((trifluoromethyl)sulfonyl)amide. The hydrophobic molten salts are promising solvents for electrochemical, photovoltaic, and synthetic applications (Bon-hote et al., 1996). 

In the Horner-Emmons reaction (Scheme 3), the sulfonylphosphonate carbanion 5 is formed in the presence of NaH and then reacts with an aldehyde to produce the intermediate 6 that undergoes in situ elimination to yield the vinyl sulfones and phosphonate anion. The sulfonyl group can stabilize the anion in the sulfonylphosphonate 5. The vinyl sulfones that are produced by this method using aldehydes as starting materials are exclusively the E (trans) isomers. The E-isomers of the vinyl sulfones are shown in the NMR spectra based on the coupling constants of the vinylic protons. Although strongly basic conditions are used in the Horner-Emmons reaction and a-amino aldehydes are easily racemized, the amino acid vinyl sulfones prepared by this method still show substantial optical activity. However, the enantiomeric purity of these compounds has not been determined. 5 ... 

The stability of the BTFP sulfonyl carbanions generated with a variety of bases including LDA, KHMDS, phosphazene bases (P4-t-Bu) and KOH-TBAB towards auto condensation was studied. It was shown that the sulfone recovery from the respective anions was higher than recovery of BT and PT sulfones. 

A sulfonyl substituent at the carbon of aziridines stabilizes the ring anion so that an alkyl moiety can be introduced at this position. As the ring is activated by the sulfonyl group, alkylated aziridines undergo a ready ring... 

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