Elimination from hydroxy acids

Lactones, l xictides, iMciams, and Lactims. When the hydroxy acid from which water may be considered to have been eliminated has a trivial name, the lactone is designated by substituting -olactone for -ic acid. Locants for a carbonyl group are numbered as low as possible, even before that of a hydroxyl group. 

Thus, in contrast to benzothiepins, dibenzo compounds can be synthesized by direct acid-catalyzed elimination of water from hydroxy derivatives, or of amines from amino derivatives, at elevated temperatures due to their thermal stability. As in the case of benzothiepins, dibenzo derivatives can also be prepared by base-catalyzed elimination from the corresponding halo derivatives however, the yields are somewhat lower compared to the acid-catalyzed reactions. As a special case, an aziridine derivative was deaminated by palladium-catalyzed hydrogenation to afford the corresponding dibenzothiepin.69... 

An interesting new method for the conversion of [I, y-epoxy sulfones (82) to cyclo-alkenones (85) has been developed61. It includes the addition of alkyllithium to y-hydroxy-a,/ -unsaturated sulfones generated from 82 and the alkylation of sulfonyl carbanion thus formed. Oxidation of the resulting y-hydroxy sulfone to 84 followed by elimination of benzenesulfinic acid gives the desired product 85 in good yields (equation 72)61. 

An OH and a COOH group can be eliminated from P-hydroxy carboxylic acids by refluxing with excess DMF dimethyl acetal. Mono-, di-, tri-, and tetrasubstituted... 

In 1929 Carothers proposed a generally useful differentiation between two broad classes of polymers condensation polymers in which the molecular formula of the structural unit (or units) lacks certain atoms present in the monomer from which it is formed, or to which it may be degraded by chemical means, and addition polymers, in which the molecular formula of the structural unit (or units) is identical with that of the monomer from which the polymer is derived. Condensation polymers may be formed from monomers bearing two or more reactive groups of such a character that they may condense intermolecu-larly with the elimination of a by-product, often water. The polyamides and polyesters referred to above afford prime examples of condensation polymers. The formation of a polyester from a suitable hydroxy acid takes place as follows ... 

Reaction of the carbanion of chloromethyl phenyl sulphoxide 409 with carbonyl compounds yields the corresponding 0-hydroxy adducts 410 in 68-79% yield. Each of these compounds appears to be a single isomer (equation 242). Treatment of adducts 410 with dilute potassium hydroxide in methanol at room temperature gives the epoxy sulphoxides 411 (equation 243). The ease of this intramolecular displacement of chloride ion contrasts with a great difficulty in displacing chloride ion from chloromethyl phenyl sulphoxide by external nucleophiles . When chloromethyl methyl sulphoxide 412 is reacted with unsymmetrical ketones in the presence of potassium tcrt-butoxide in tert-butanol oxiranes are directly formed as a mixture of diastereoisomers (equation 244). a-Sulphinyl epoxides 413 rearrange to a-sulphinyl aldehydes 414 or ketones, which can be transformed by elimination of sulphenic acid into a, 8-unsaturated aldehydes or ketones (equation 245). The lithium salts (410a) of a-chloro-/ -hydroxyalkyl... 

Chromanoxylium cation 4 preferably adds nucleophiles in 8a-position producing 8a-substituted tocopherones 6, similar in structure to those obtained by radical recombination between C-8a of chromanoxyl 2 and coreacting radicals (Fig. 6.4). Addition of a hydroxyl ion to 4, for instance, results in a 8a-hydroxy-tocopherone, which in a subsequent step gives the /zara-tocopherylquinone (7), the main (and in most cases, the only) product of two-electron oxidation of tocopherol in aqueous media. A second interesting reaction of chromanoxylium cation 4 is the loss of aproton at C-5a, producing the o-QM 3. This reaction is mostly carried out starting from tocopherones 6 or /zora-tocopherylquinone (7) under acidic catalysis, so that chromanoxylium 4 is produced in the first step, followed by proton elimination from C-5a. In the overall reaction of a tocopherone 6, a [ 1,4] -elimination has occurred. The central species in the oxidation chemistry of a-tocopherol is the o-QM 3, which is discussed in detail subsequently. 

Additional hypotheses concerning prostaglandin biosynthesis in P. homomalla resulted from isolation of 11R-HETE (76) from the polar lipid fraction [95]. Apparently, 11R-HETE (76) is also a minor product of incubations of arachidonic acid with acetone powder preparations of P. homomalla [95], In this alternate hypothesis (Scheme 8), an 11-hydroxy or 11-hydroperoxy-8,9-allene oxide intermediate is formed from a sequence of oxidations at C8 and Cll. Opening of the allene oxide to a transient C8 earboeation induces eycli-zation with a consequent addition of water to C15. This proposed pathway leads initially to formation of PGE2 (16 or 38), which following acetylation, elimination of acetic acid from Cl 1-12, and esterification, forms the observed major natural product in the coral, 15-acetoxy methyl PGA2 (36 or 54). Notably, if... 

Metabolism of the 2,S -isomers proceeds sequentially hydroxylation at the phenoxy group, hydrolysis of the cyano group, and cleavage of the ester linkage (Coats et al. 1989). Fenvalerate and the IS-isomers yield two ester metabolites in feces from hydroxylation at the 4 - and 2 -phenoxy positions. Other significant metabolites were 3-phenoxybenzoic acid and its hydroxy derivatives from the alcohol moiety, 3-(4-chlorophenyl) isovaleric acid and its hydroxy derivatives from the acid moiety, and thiocyanate and carbon dioxide from the cyano moiety (Ohkawa et al. 1979). A slow elimination rate characterizes fenvalerate and other a-cyano pyrethroids when compared with... 

A xanthone also results from the cyclization of 2 -nitro-6-hydroxy-2,4-dimethoxyben-zophenone, which is the sole product from a photo-Fries rearrangement of 3,5-dimethoxyphenyl 2-nitrobenzoate (81T209). Ring closure is effected in boiling piperidine and appears to involve elimination of nitrous acid together with ether cleavage. 

Polymer synthesis by step-reaction involves the coupling of small molecules which are difunctional by virtue of having two reactive functional groups. It is common for the coupling to involve elimination of a small molecule, and typical examples might be the synthesis of a polyester from a hydroxy-acid or of a polyamide by reaction of a diamine with a diacid. Step-reaction polymerizations are often equilibria, whereas chain-reaction polymerizations are more usually irreversible. 

The transient zwitterion (15), obtained from the /(-hydroxy acid precursor by laser flash photolysis, has been characterized 46 it reacts with nucleophiles more slowly than does the 9-fluorenyl cation itself. The parent acid was also characterized.46 Evidence has been presented that (16) undergoes substantial El elimination via a primary carbocation.47 An analysis of solvolysis results for (17) is indicative of extensive charge delocalization throughout the fluorenyl ring at the transition state apparently... 

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