Sulfoxide dehydration

Sulfoxide dehydration. When a mixture of the sulfoxide l,3-dihydrobenzo[f]-thiophene 2-oxide and grade 1 neutral alumina (Woelm) is heated under 25-mm. pressure at 12U-130° in a sublimer, almost pure benzo[c]thiophcnc (2) condenses on the... 

The widely used Moifatt-Pfltzner oxidation works with in situ formed adducts of dimethyl sulfoxide with dehydrating agents, e.g. DCC, AcjO, SO], P4O10, CCXTl] (K.E, Pfitzner, 1965 A.H. Fenselau, 1966 K.T. Joseph, 1967 J.G. Moffatt, 1971 D. Martin, 1971) or oxalyl dichloride (Swem oxidation M. Nakatsuka, 1990). A classical procedure is the Oppenauer oxidation with ketones and aluminum alkoxide catalysts (C. Djerassi, 1951 H. Lehmann, 1975). All of these reagents also oxidize secondary alcohols to ketones but do not attack C = C double bonds or activated C —H bonds. 

Perchloric acid Acetic acid, acetic anhydride, alcohols, antimony compounds, azo pigments, bismuth and its alloys, methanol, carbonaceous materials, carbon tetrachloride, cellulose, dehydrating agents, diethyl ether, glycols and glycolethers, HCl, HI, hypophosphites, ketones, nitric acid, pyridine, steel, sulfoxides, sulfuric acid... 

Trifluoromethanesulfonic acid is miscible in all proportions with water and is soluble in many polar organic solvents such as dimethylformamide, dimethyl sulfoxide, and acetonitrile. In addition, it is soluble in alcohols, ketones, ethers, and esters, but these generally are not suitably inert solvents. The acid reacts with ethyl ether to give a colorless, Hquid oxonium complex, which on further heating gives the ethyl ester and ethylene. Reaction with ethanol gives the ester, but in addition dehydration and ether formation occurs. 

In addition to the synthetic applications related to the stereoselective or stereospecific syntheses of various systems, especially natural products, described in the previous subsection, a number of general synthetic uses of the reversible [2,3]-sigmatropic rearrangement of allylic sulfoxides are presented below. Several investigators110-113 have employed the allylic sulfenate-to-sulfoxide equilibrium in combination with the syn elimination of the latter as a method for the synthesis of conjugated dienes. For example, Reich and coworkers110,111 have reported a detailed study on the conversion of allylic alcohols to 1,3-dienes by sequential sulfenate sulfoxide rearrangement and syn elimination of the sulfoxide. This method of mild and efficient 1,4-dehydration of allylic alcohols has also been shown to proceed with overall cis stereochemistry in cyclic systems, as illustrated by equation 25. The reaction of trans-46 proceeds almost instantaneously at room temperature, while that of the cis-alcohol is much slower. This method has been subsequently applied for the synthesis of several natural products, such as the stereoselective transformation of the allylic alcohol 48 into the sex pheromone of the Red Bollworm Moth (49)112 and the conversion of isocodeine (50) into 6-demethoxythebaine (51)113. 

ABSTRACT Zeolite Y modified with chiral sulfoxides has been foimd catal rtically to dehydrate racemic butan-2-ol enantioselectively depending on the chiral modifier used. Zeolite Y modified with R-l,3-dithiane-1-oxide shows a higher selectivity towards conversion of S-butan-2-ol and the zeolite modified with S-2-phenyl-3-dithiane-1-oxide reacts preferentially with R-butan-2-ol. Zeolite Y modified with dithiane oxide demonstrates a significantly higher catalsdic activity when compared to the unmodified zeolite. Computational simulations are described and a model for the catalytic site is discussed. 

In contrast, synthesis of 3,4-diphosphorylthiophenes requires more elaboration because of low reactivity of 3,4-positions of thiophene and unavailability of 3,4-dihalo or dimetallated thiophenes. Minami et al. synthesized 3,4-diphosphoryl thiophenes 16 as shown in Scheme 24 [46], Bis(phosphoryl)butadiene 17 was synthesized from 2-butyne-l,4-diol. Double addition of sodium sulfide to 17 gave tetrahydrothiophene 18. Oxidation of 18 to the corresponding sulfoxide 19 followed by dehydration gave dihydrothiophene 20. Final oxidation of 20 afforded 3,4-diphosphorylthiophene 16. 3,4-Diphosphorylthiophene derivative 21 was also synthesized by Pd catalyzed phosphorylation of 2,5-disubstituted-3,4-dihalothiophene and converted to diphosphine ligand for Rh catalysts for asymmetric hydrogenation (Scheme 25) [47],... 

Oxidation of tetraphosphoryldihydrothiophene 23 with one equivalent of mCPBA gave corresponding sulfoxide 28 as an initial product, which was dehydrated during chromatographic separation to give tetraphosphorylthiophene 13 (Scheme 29). On the other hand, oxidation with excess mCPBA gave sulfone 29 as a stable product. 

Pummerer-type dehydration of the sulfoxide 408 using acetic anhydride results in efficient formation of the 1,3-dipolar compound 409 which is able to undergo cycloaddition with dienophiles to generate tricyclic compounds such as 410 in good yield (Scheme 31) <2000T10011>. 

Oxidation of sulfur atom of pyrazolo[l,5-c]thiazole 64 into sulfoxide 65 followed by Pummerer-type dehydration furnished the transient nonclassical pyrazolo[ 1,5-c]thiazole, the thiocarbonyl ylide 67, which could react with various dipolarophiles such as Ar-pheny 1 ma 1 eiinide (Equations 27 and 28) <2000T10011>. In an excess of oxidizing agent, pyrazolo[l,5-c]thiazole 64 was readily converted to sulfone 66 (Equation 27) <2001J(P1)1795>. 

Dehydrating agents have commonly been employed in the preparation of lanthanide sulfoxide complexes from hydrated lanthanide salts. For example, dimethoxypropane has been used to prepare both (CH2)4SO (65) and rePr2SO (56) complexes of the lanthanide nitrates. An alternative dehydrating agent is ethyl orthoformate [Eq. (14)]. 

This powerful dehydrating agent was initially used in the preparation of nickel sulfoxide complexes (244), but has found wider application in the chemistry of lanthanide sulfoxide complexes (189). 

Continuing their search for ways to synthesize this system. Cava and Husbands " allowed tetrabenzoylethane (146) to react with phosphorus pentasulfide in refluxing xylene to obtain 46% of 1,3,4,6-tetraphenyl-li/,3if-thieno[3,4-c]thiophene (147) oxidized with periodate the latter yielded the sulfoxide (148), which was dehydrated with acetic anhydride to produce the stable l,3,4,6-tetraphenylthieno[3,4-c]thiophene (149) (87%). The latter is obtained in one step, in about 3% yield, by the reaction of tetrabenzoylethane (146) with phosphorus pentasulfide in refluxing xylene, along with the formation of 147 (30%). A mixture of two ad-... 

In 1973 Cava et al. reported the synthesis of 4,6-dimethyl-l/f,3if-thieno[3,4-c]thiophene (142) and l,3,4,6-tetraphenylthieno[3,4-cl-thiophene (149) ° as well as data on some chemicaJ conversions of the latter and the dehydration of 4,6-dimethoxycarbonyl-l/f,3H-thieno-[3,4-c]thiophene sulfoxide. Thienothiophene (149) was also obtained (42%) by Potts and McKeough by condensation of anhydro-4-hydroxy-2,3,5-triphenylthiazolium hydroxide with dibenzoylacetylene followed by reaction of the product with P S,. 

If the water content is driven off (usually by heating to 350 °C in a vacuum), the dehydrated zeolite becomes an avid absorber of small molecules, especially water. The size of the molecules that can be absorbed is limited by the zeolite pore diameter, which is different for different zeolites (Table 7.1) a given zeolite (e.g., zeolite 3A) can be a highly selective absorber of, say, small amounts of water from dimethyl sulfoxide (DMSO) solvent. For this reason, dehydrated zeolites are often called molecular sieves. 

The classical synthetic pathway to prepare polyimides consists of a two-step scheme in which the first step involves polymerization of a soluble and thus processable poly(amic acid) intermediate, followed by a second dehydration step of this prepolymer to yield the final polyimide. This preparative pathway is representative of most of the early aromatic polyimide work and remains the most practical and widely utilized method of polyimide preparation to date. As illustrated in Scheme 4, this approach is based on the reaction of a suitable diamine with a dianhydride in a polar, aprotic solvent such as dimethyl sulfoxide (DMSO), dimethylacetamide (DMAc), dimethylformamide (DMF), or AT-methylpyrrolidone (NMP), generally at ambient temperature, to yield a poly(amic acid). The poly(amic acid) is then cyclized either thermally or chemically in a subsequent step to produce the desired polyimide. This second step will be discussed in more detail in the imidization characteristics section. More specifically, step 1 in the classical two-step synthesis of polyimides... 

These unusual sulfur heterocycles (310 R = H,Ph) have been generated in situ by Pummerer dehydration of the sulfoxides 312 (R = H, Ph). Isolation of the betaines has not been achieved, but they are trapped in high yield by A -phenylmaleimide giving the exo adducts (313 R = H, Ph, R = This is in sharp contrast to the corresponding nitrogen... 

Whereas compounds of type 345 are not known, the transient existence of tetraphenylthieno[3,4- ]furan (348) has been demonstrated. Sulfoxide 347 refluxed in acetic anhydride under nitrogen gave a pale violet color which was attributed to 348 in the presence of dimethyl acetylenedicar-boxylate a Diels-Alder adduct (349) was formed in 70% yield. 76-479 dehydration of 347 can also be effected by base treatment with hydroxide ion in benzene/water with a phase-transfer catalyst affords a deep-blue... 

An unusual dehydration reaction was observed in the case of sulfoxide 290, which yielded 99% of 2//-thiopyran 291 on heating with acetic anhydride.302... 

When /3-vinylbutenolide (158), prepared from /3-vinylbutyrolactone by a sulfenylation-sulfoxide elimination process, was reacted with the anion of a-methylcyclohexane-1,3-dione, two products (159) and (160) were produced in an 11 1 ratio (47% combined yield) (75CC337). Dehydration of these compounds with thionyl chloride in pyridine yielded (161) and (162), respectively (Scheme 35). The annelation products are useful intermediates for sesquiterpene lactone construction. 

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