Sulfoxides, isomerization

The combination of potassium /butoxide with dimethyl sulfoxide isomerizes the... 

Platinum. dichlorobis(dimethyl sulfoxide)-isomerization, 320 Platinum, dichlorobis(pyridine)-... 

Bergson et /.i4 i8,247.248.3i4 using mr spectrometry and polarimetry as analytical techniques, made a detailed study of the kinetics and mechanisms of base-catalyzed isomerization, racemization, and mutarotation reactions of 1-substituted and 1,3-disubstituted indenes. The prototropic rearrangements are completely stereospecific and intramolecular when aliphatic amines are used as catalysts in solvents of low or moderate polarity— the proton becomes re-attached to the same side of the ring system from which it departed under these conditions With alcohols as solvents and alkoxides as catalysts, extensive racemization occurs indicating that indenes form symmetrically solvated carbanions in alcohol solvents. In dimethyl sulfoxide, isomerization was only partly stereospecific even when aliphatic amines were used as catalysts. These, and other observations, are rationalized by the reaction scheme... 

Knoevenagel CondensationA/inyl Sulfoxide Isomerization/Mislow-Evans... 

Vinyl sulfoxide isomerization followed by Mislow-Evans rearrangement was also central to a S5mthetic route toward the hydroazulene moiety of the antibiotic fungal metabolite guanacastepene A fScheme 18.611. In this case, a diastereomeric mixture of vinyl sulfoxides 241 resulted upon oxidation of the starting vinyl sulfide 240. Subsequent treatment with DBU led to the sequential isomerization/[2,31-rearrangement process. Under these conditions, the intermediate sulfenate was converted to the allylic alcohol 242, produced as a 4 1 mixture of epimers. Here, the modest selectivity in formation of the allylic stereocenter was of no synthetic consequence, as the alcohol was subsequendy oxidized to the corresponding enone. Notably, the overall conversion from 240 to 242 represents a 1,3-vinyl-to-allyl heteroatom transposition. 

Rack JJ (2009) Electron transfer triggered sulfoxide isomerization in ruthenium and osmium complexes. Coord Chem Rev 253 78-85... 

Note 2. Traces of unreacted triethylamine might cause partial isomerization of the allenyl sulfoxide into the propargyl sulfoxide. The methyl iodide is added to ensure that no triethylamine remains. 

A new, versatile and selective synthesis of 6- and 7-substituted pteridines was reported by Rosowsky (73JOC2073). /3-Keto sulfoxides, which can be viewed as latent a keto aldehydes, react with (251) to give 6-substituted pterins, and the use of a-keto aldehyde hemithioacetals leads in a regiospecific synthesis to the isomeric 7-substituted pterins (equation 85). 

The direct combination of selenium and acetylene provides the most convenient source of selenophene (76JHC1319). Lesser amounts of many other compounds are formed concurrently and include 2- and 3-alkylselenophenes, benzo[6]selenophene and isomeric selenoloselenophenes (76CS(10)159). The commercial availability of thiophene makes comparable reactions of little interest for the obtention of the parent heterocycle in the laboratory. However, the reaction of substituted acetylenes with morpholinyl disulfide is of some synthetic value. The process, which appears to entail the initial formation of thionitroxyl radicals, converts phenylacetylene into a 3 1 mixture of 2,4- and 2,5-diphenylthiophene, methyl propiolate into dimethyl thiophene-2,5-dicarboxylate, and ethyl phenylpropiolate into diethyl 3,4-diphenylthiophene-2,5-dicarboxylate (Scheme 83a) (77TL3413). Dimethyl thiophene-2,4-dicarboxylate is obtained from methyl propiolate by treatment with dimethyl sulfoxide and thionyl chloride (Scheme 83b) (66CB1558). The rhodium carbonyl catalyzed carbonylation of alkynes in alcohols provides 5-alkoxy-2(5//)-furanones (Scheme 83c) (81CL993). The inclusion of ethylene provides 5-ethyl-2(5//)-furanones instead (82NKK242). The nickel acetate catalyzed addition of r-butyl isocyanide to alkynes provides access to 2-aminopyrroles (Scheme 83d) (70S593). 

Isomerization of 3-cephems (27) to 2-cephems (28) takes place in the presence of organic bases (e.g. pyridine) and is most facile when the carboxyl is esterified. Normally an equilibrium mixture of 3 7 (3-cephem/2-cephem) is reached. Since the 2-cephem isomers are not active as antibacterial agents, the rearrangement proved to be an undesirable side reaction that complicated acylation of the C-7 amine under certain conditions. A method for converting such mixtures to the desired 3-cephem isomer involves oxidation with concomitant rearrangement to the 3-cephem sulfoxide followed by reduction. Additions... 

Extension of the above method to 3-methoxyestra-3,5(10)-dien-17-one 17-ethylene ketal (46) prepared by base-catalyzed isomerization of 3-methoxy-estra-2,5(10)-dien-17-one 17-ketal (42) with potassium t-butoxide in dimethyl sulfoxide gives the isomeric tropone A-homo-estra-l,4,5(10)-triene-3,17-dione... 

When 1,2-dibromodecane was treated with potassium hydroxide in aqueous ethanol, it yielded a mixture of three isomeric compounds of molecular formula CioHi9Br. Each of these compounds was converted to 1-decyne on reaction with sodium amide in dimethyl sulfoxide. Identify these three compounds. 

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

Compound 6 crystallizes from cyclohexane as colorless needles which have no definite melting point there is a change of color to yellow at 128-134 C and the compound then melts sharply at 187-189 r C. When the colorless form is kept for a long time or recrystallized from pyridine or dimethyl sulfoxide it is changed into the yellow modification of mp 187-189 C recrystallization from cyclohexane reverses the process. It has been suggested that the yellow stable form has structure 6A and that the colorless metastable compound is the tautomer 2-methyl-l//-pyrido[2,3-6][l, 4]diazepin-4(5//)-one (6B). There is evidence from 1H NMR spectroscopy that the isomeric pyridodiazepin-2-one, yellow crystals, mp 195—197 " C, exists as an inseparable mixture of the tautomers 4-methyl-l//-pyrido[2,3-6][l,4]diazepin-2(3//)-one (7 A) and 4-methyl-l H-pyrido[2,3-6][l, 4Jdiazepin-2(5//)-one (7B) in the ratio 1 3. 

Thiopyrans 169 have been reported to isomerize to thiophenes 170 on heating in ethanol (90TL115). The sulfoxide 47b was found to afford 2//-thiopyran isomer 171 on heating in AcOH but another 4//-thiopyran,... 

As shown in Table 4, the same ratio of diastcreomeric sulfinylalkcnols was obtained from both (R)-(E)- and (/ )-(Z)-l-sulfinylalkenes (vinyl sulfoxides). This is explained by the fast cisjtrans isomerization of the organolithium intermediates in a strongly basic medium. Thus, EjZ mixtures of vinyl sulfoxides can be used without prior separation. 

The reaction of the anion of an aryl allyl sulfoxide with benzaldehyde can take place via an a or y attack. The a attack leads to a product with three stercogcnic centers (four possible diastereomers) whereas the y attack results in a product which has only two stereogenie centers and geometric isomerism is possible. 

Isomeric (E)- and (Z)-a,/f-unsaturated sulfoxides undergo addition with opposite dia-stereoselectivities. 

Chromium, hexacyano-, 3, 703, 777 hexaamminecobaltate coordination isomerism, 1, 183 ligand field photochemistry, 1, 398 photochemistry excited states, 1, 398 production, 3, 704 Chromium, hexafluoro-, 3, 927 Chromium, hexabalo-, 3, 889 Chromium, hexaiodo-, 3, 766 Chromium, hexakis(dimethyl sulfoxide)-photoanation, 1, 399 Chromium, u-oxalatodi-reduction... 

Since sulfoxides and sulfones are versatile synthetic intermediates, and since in both the thiolene oxide and dioxides the reverse dethionylation114 ( — SO), and cheletropic extrusion of sulfur dioxide296, respectively, readily take place thermally, these cycloadditions are expected to find a useful place in organic synthesis. It should be kept in mind, however, that the retrograde SO-diene reaction and interconversion of the thiolene oxides compete effectively against SO extrusion on heating, and that diene isomerization accompanies the forward reaction (SO + diene). 

A final, rather different example which fits in appropriately here, in that it involves hydrogen exchange, is the measurement of equilibrium and rate constants for the base-catalyzed isomerization of unsaturated sulfides, sulfoxides and sulfones193 ... 

Benzhydryl trichloromethanesulfenate rearranged to the corresponding sulfoxide after 10 min of reflux of a hexane solution, while the benzyl ester remained practically unchanged even after heating for 24 h at 120°C in benzene. Isomerization of optically active ( — )-a-phenylethyl trichloromethanesulfenate, [a]D20 = — 20.5° on heating in... 

In contrast to the allylic sulfenates mentioned so far, cinnamyl trichloromethanesulfenate (9), prepared by the usual method, can be isolated and is relatively stable. Furthermore, its rearrangement to cinnamyl trichloromethyl sulfoxide (i.e., without allylic isomerization, equation 7), proceeds at a relatively slow rate (in CC14 at 80.0 °C, k = 3.90 x 10 5s 1). This result also contrasts with the observation mentioned earlier that cinnamyl arenesulfinate rearranges to a-phenylallyl aryl sulfone33,34. Similar behavior has been detected for y, y-dimethylallyl ester 11 which undergoes thermal isomerization to sulfoxide 12 (equation 8)36-38. 

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