Sulfones, addition-trapping

Watanabe et al. examined a similar addition/trapping tandem involving vinylic sulfones [178]. Acceptable ee s were obtained when bidentate chelation was made possible, as was the case when benzimidazolyl moities were attached to the sulfur atom (the ligand was again a box derivative). Yet only one stereogenic center was created during the reaction. 

Oxidation of thiophene with peracid under carefully controlled conditions gives a mixture of thiophene sulfoxide and 2-hydroxythiophene sulfoxide. These compounds are trapped by addition to benzoquinone to give ultimately naphthoquinone (225) and its 5-hydroxy derivative (226) (76ACS(B)353). The further oxidation of the sulfoxide yields the sulfone, which may function as a diene or dienophile in the Diels-Alder reaction (Scheme 88). An azulene synthesis involves the addition of 6-(A,A-dimethylamino)fulvene (227) to a thiophene sulfone (77TL639, 77JA4199). 

Potassium or lithium derivatives of ethyl acetate, dimethyl acetamide, acetonitrile, acetophenone, pinacolone and (trimethylsilyl)acetylene are known to undergo conjugate addition to 3-(t-butyldimethylsiloxy)-1 -cyclohexenyl t-butyl sulfone 328. The resulting a-sulfonyl carbanions 329 can be trapped stereospecifically by electrophiles such as water and methyl iodide417. When the nucleophile was an sp3-hybridized primary anion (Nu = CH2Y), the resulting product was mainly 330, while in the reaction with (trimethylsilyl)acetylide anion the main product was 331. 

The conjugate addition of tributylstannylmethyllithium to unsaturated sulfones 100, followed by trapping with an aldehyde, provides a route to the allyl alcohol 101 which may be transformed into 2(5H)-furanones (equation 81)67. 

Silylcuprates have been reported to undergo reactions with a number of miscellaneous Michael acceptors [65]. Conjugate addition to 3-carbomethoxy acyl pyri-dinium salts [65a] affords 4-silyl-l,4-dihydropyridines. Oxidation with p-chlorand generates a 4-acyl pyridinium salt that gives the 4-silylnicotinate upon quenching with water, and methyl 4-silyl-2-substituted dihydronicotinates upon quenching with nucleophiles (nucleophilic addition at the 6-position). The stabilized anion formed by conjugate addition to an a, j8-unsaturated sulfone could be trapped intramolecularly by an alkyl chloride [65b]. 

An additional means of performing a selective cross-benzoin was reported in 2001 when Mnrry and co-workers expanded benzoin methodology to include trapping of acyl imines XIX formed in situ (Scheme 6) [53], The authors chose to use a-amido sulfones due to their stability and the relative ease of acyl imine liberation. The parent reaction combines pyridine 4-carboxaldehyde 51 and tosylamide 52 in 98% yield in the presence of pre-catalyst 54 and triethylamine (Scheme 6). 

A preferred synthetic procedure to PAEH concerns the formation of the bisphenolate salt followed by the addition of the activated difluoro, dichloro or dinitro monomer. As an example, the heterocyclic bisphenol is stirred in a mixture of toluene and an aprotic polar solvent such as DMAc, NMP or diphenyl sulfone at 135-140 °C for several hours in the presence of 10 mol % excess of powdered anhydrous potassium carbonate (stoichiometric amount of sodium or potassium hydroxide can be used) under a Dean-Stark trap in a nitrogen atmosphere. Water is removed by azeotropic distillation. A stoichiometric quantity of the difluoro monomer is then added to the slightly cooled reaction mixture. The toluene is removed and the reaction is stirred at 155°C in DMAc for one to several hours. Polymer isolation is performed as previously described. This procedure minimizes hydrolysis of the difluoro monomer, gel formation and molecular weight equilibration of the polymer. 

Hydrogenolysis of vinyl sulfones.2 Vinyl sulfones are reduced by Na2S204 and NaHC03 in aqueous ethanol with retention of configuration. The reaction is facilitated by use of a phase-transfer catalyst such as Adogen. The reduction involves addition of HSOz to form a sulfone sulfinate salt which can be trapped by CH3I. The overall reaction thus involves a (3-syn-addition followed by an anti-elimination. This hydrolysis was used in a synthesis of several insect pheromones, such as (Z)-8-dodecenyl-l-acetate (1). 

The term hard-core RMs is used to describe dispersions containing an excess of colloidal carbonate over that required to neutralize the sulfonic acid. The excess is found in calcium carbonate trapped in a micellar structure. The total base number (TBN) of the additive so obtained is 368 mg KOH/g of oil. The crude additive consisted of 33 wt% CaC03 (Delfort et al., 1995 Giasson et al., 1992). Some typical results of the core particle with the overall diameter and the detergent layer thickness are shown in Table 3.6 (Marsh, 1987). 

The first step in this multistage reaction is the nucleophilic addition of sulfone anion 28 to aldehyde 8 (Scheme 14.6). This produces a p-alkoxysulfone intermediate 29 which is trapped with acetic anhydride. The resulting P acetoxysulfone mixture 22 is then subjected to a reductive elimination with Na/Hg amalgam to obtain alkene 23. The tendency of Julia-Lythgoe-Kocienski olefinations to provide ( )-1,2-disubstituted alkenes can be rationalised if one assumes that an a-acyloxy anion is formed in the reduction step, and that this anion is sufficiently long-lived to allow the lowest energy conformation to be adopted. Clearly, this will... 

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