Dialkyl sulfoxide

Tai156 applied MM2 to the ten dialkyl sulfoxides possible when the alkyl groups are restricted to methyl, ethyl, isopropyl and t-butyl, and calculated that only one or two conformations exist in substantial amount (> 20%) for each molecule. 

A method for the stereospecific synthesis of thiolane oxides involves the pyrolysis of derivatives of 5-t-butylsulfinylpentene (310), and is based on the thermal decomposition of dialkyl sulfoxides to alkenes and alkanesulfenic acids299 (equation 113). This reversible reaction proceeds by a concerted syn-intramolecular mechanism246,300 and thus facilitates the desired stereospecific synthesis301. The stereoelectronic requirements preclude the formation of the other possible isomer or the six-membered ring thiane oxide (equation 114). Bicyclic thiolane oxides can be prepared similarly from a cyclic alkene301. 

The total yield of sulfinic acid from the mixed sulfoxides is higher than that from diphenyl sulfoxides (31%) but lower than that from the corresponding dialkyl sulfoxides, and accounts for about 45% of the OH radicals (Table 1). 

B. Radical Anions of Dialkyl Sulfoxides and Dialkyl Sulfones.1053... 

The radical anions of dialkyl sulfoxides (or sulfones) may be obtained by direct capture of electron during y-irradiation. It was shown that electron capture by several electron acceptors in the solid state gave anion adducts 27. It was concluded276 that these species are not properly described as radical anions but are genuine radicals which, formed in a solid state cavity, are unable to leave the site of the anions and exhibit a weak charge-transfer interaction which does not modify their conformation or reactivity appreciably, but only their ESR spectra. For hexadeuteriodimethyl sulfoxide in the solid state, electron capture gave this kind of adduct 278,28 (2H isotopic coupling 2.97 G is less than 3.58 G normally found for -CD3). 

The sulfenic acids have been found to be extremely active radical scavengers showing rate constants of at least 107 m"1 s 1 for the reactions with peroxyl radicals at 333 K17. It has also been suggested that the main inhibiting action of dialkyl sulfoxides or related compounds in the autoxidation of hydrocarbon derives from their ability to form the transient sulfenic acids on thermal decomposition, i.e.17... 

A major problem with the sulfoxide synthesis using menthyl sulfmates is its failure to produce optically pure dialkyl sulfoxides. The prerequisite menthyl alkanesulfinates are oils which have resisted separation into the individual epimers. The menthyl phenyl methanesulfmates are an exception the R epimer is crystalline . One solution to this problem, at least for preparing methyl alkyl sulfoxides, was achieved using cholesteryl methanesulfmates (27) . Both epimers were crystalline and could be separated by fractional crystallization, although in poor yield. Treatment of the epimers with n-propyl, n-butyl, isobutyl, p-tolyl and benzyl magnesium halides yielded the respective methyl alkyl sulfoxides (28) in greater than 95% e.e. and in 32 to 53% yields. 

Potzinger and coworkers determined ionisation and appearance energies for the molecular and major fragment ions of several dialkylsulfoxides, R SOR (R =Me R = Me, Et, i-Pr, and i-pentyland R = R = Et or i-Pr). In addition to the evaluation of dissociation energies in the ions and their enthalpies of formation, a value of 280 + 30kJmol" for the C—S dissociation energy in neutral dialkyl sulfoxides was derived. 

The above procedure can be exploited for the asymmetric oxidation of racemic sulfoxide1 1, and high stereoselection can be frequently observed. Moreover unreacted / -sulfoxides were always recovered as the most abundant enantiomers, kinetic resolution and asymmetric oxidation being two enantioconvergent processes. Thus, by the combined routes, higher enantioselectivity can be observed with dialkyl sulfoxides, usually obtained with poor to moderate e.e.s. 

To summarize, free sulfoxides carry a net positive charge on the sulfur atom which (1) is independent of chain length in dialkyl sulfoxides, (2) is greater for dialkyl sulfoxides than diaryl sulfoxides, (3) is virtually unaltered by O-bonding, and (4) is increased by S-bonding. 

No sulfoxide complexes of osmium have been reported. Unsymmetri-cal dialkyl sulfoxides have been utilized in extraction studies, and methyl-4,8-dimethylnonyl sulfoxide has found application in the extraction of iron (266). Extraction of ruthenium from hydrochloric acid solutions by sulfoxides has been studied (470) and comparisons of sul-fones, sulfoxides, and thioethers as extractants for nitrosoruthenium species reported (441, 443). Similar studies on the extraction of nitro-soosmium species have been reported (442). 

Optically active dialkyl sulfoxides of high optical purity (>95%), which could not be prepared from menthyl alkanesulfmates, have been synthesized by Johnson et al. (93) via reaction of chiral alkyl aryl sulfoxides with alkyllithium reagents. The exchange of the... 

All diaryl sulfoxides, some alkyl aryl sulfoxides (e.g., methyl p-tolyl sulfoxide, 41), and some dialkyl sulfoxides (e.g., methyl 1-adamantyl sulfoxide), were found to undergo racemization according to the pyramidal inversion mechanism. Mislow and co-workers (248) have found that for most of the compounds investigated, irrespective of the nature of the substituents attached to sulfur, the first-order rate constant for racemization in p-xylene at 210 C is about 3 X 10" sec", corresponding to a half-life of about 6 hr. Moreover, the activation parameters do not show significant differences and their values were contained in a narrow range 35 to 42 kcal/mol and... 

Grignard exchange reactions of sulfoxides substituted with groups other than azaheterocycles proceed mostly by an inversion on the sulfur atom there are a few exceptions (73S485 74CJC761). As shown in reactions (15) and (16), optically active dialkyl sulfoxides can be prepared starting from... 

Another new application has been the use of complexes such as Ni(acac)2 and Pd(acac)2, as catalysts in the fragmentation of dialkyl sulfoxides, which yielded reactive thials isolated by reaction with 1,3-dienes330 (equation 61). 

Colonna S, Gaggero N, Carrea G, Pasta P (1997) A New Enzymatic Enantioselective Synthesis of Dialkyl Sulfoxides Catalysed by Monooxygenases. Chem Commun 439... 

A series of [3-carbonyl sulfides was studied as substrates for CPO-catalyzed oxygenation (Scheme 2.16) [238]. The corresponding dialkyl sulfoxides formed quantitatively if R2 is methyl or ethyl, but the yields drop dramatically for larger substituents. The steric control was present also in cyclic derivatives where the cyclohexanone residue results in about a 50% reduction in yield with respect to the smaller cyclopentanone. Surprisingly, the y-butyrolactone produces the sulfoxide in quantitative amounts [239]. A similar result was obtained with benzo[fo]thiophenes as substrates [240]. 

Toda, F., Tanaka, K., and Nagamatsu, S. (1984) Mutual Optical Resolution of 2,2 -Dihydroxy-l, 1 -binaphthyl and Alkyl Aryl or Dialkyl Sulfoxides by Complex Formation, Tetrahedron Lett., 25, 4929-4932. 

Chiral sulfoxides are useful intermediates in asymmetric synthesis. A number of methods for their preparation were developed in the last decade. An interesting displacement of dimethylphosphonylmethyl moiety, a carbon leaving group, from sulfur by Grignard reagents was used to obtain enantiomerically purep-tolyl sulfoxides.3 4 Optically pure methyl 4-bromophenyl sulfinate was subjected to a one-pot sequence yielding unsymmetrical dialkyl sulfoxides in 60-97% yield and >98% ee. A simple one-pot synthesis of chiral sulfoxides from norephedrine-derived... 

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