Hydroxy mercuration

Zinc carboxylates are prepared in aqueous ethanol solution by sonication of zinc carbonate in the presence of the acid.1 2 Only 5-min irradiation times are required, and the method was successfully applied to Boc-protected amino acids (p. 147). Mercuric carboxylates were prepared from yellow mercuric oxide and carboxylic acids.43 The sonochemical reaction proceeds very fast in apolar solvents, and a series of salts were prepared by this method and used in hydroxy-mercuration reactions. This reaction can be effected directly from a mixture of the olefin, mercuric oxide, and a carboxylic acid (p. 119). 

In the presence of mercuric salts, butynediol rapidly isomerizes to 1-hydroxy-3-buten-2-one (62). 

Biacetyl is produced by the dehydrogenation of 2,3-butanediol with a copper catalyst (290,291). Prior to the availabiUty of 2,3-butanediol, biacetyl was prepared by the nitrosation of methyl ethyl ketone and the hydrolysis of the resultant oxime. Other commercial routes include passing vinylacetylene into a solution of mercuric sulfate in sulfuric acid and decomposing the insoluble product with dilute hydrochloric acid (292), by the reaction of acetal with formaldehyde (293), by the acid-cataly2ed condensation of 1-hydroxyacetone with formaldehyde (294), and by fermentation of lactic acid bacterium (295—297). Acetoin [513-86-0] (3-hydroxy-2-butanone) is also coproduced in lactic acid fermentation. 

Methylation of avermectins B and B2 leads to the corresponding derivatives of the A series (49). A procedure involving the oxidation of the 5-methoxy group with mercuric acetate and NaBH reduction of the 5-keto-intermediate allows the conversion of the A to the B components (50). The 23-hydroxy group of the "2" components, after selective protection of the other secondary hydroxy groups, is converted to a thionocarbonate, which can be elirninated to give the 22,23-double bond of the "1" components alternatively it can be reduced with tributyltin hydride to the 22,23-dihydro derivatives (= ivermectins) (51). 

Selenophene, 2,5-dimethyl-3-mercapto-synthesis, 4, 956 tautomerism, 4, 946 Selenophene, 2,4-diphenyl-synthesis, 4, 135 Selenophene, 2,5-diphenyl-lithiation, 4, 949 UV spectra, 4, 941 Selenophene, 2-ethoxycarbonyl-mercuration, 4, 946 Selenophene, halo-reactions, 4, 955 Selenophene, 2-hydroxy-Michael reaction, 4, 953 tautomerism, 4, 36, 945, 953 Selenophene, 3-hydroxy-tautomerism, 4, 36, 945 Selenophene, 3-hydroxy-2,5-dimethyl-tautomerism, 4, 945, 953 Selenophene, 2-hydroxy-5-methyl-methylation, 4, 953 tautomerism, 4, 945 Selenophene, 2-hydroxy-5-methylthio-tautomerism, 4, 945 Selenophene, 3-iodo-synthesis, 4, 955 Selenophene, 3-lithio-reactions, 4, 79 synthesis, 4, 955 Selenophene, 2-mercapto-tautomerism, 4, 38 Selenophene, 3-mercapto-tautomerism, 4, 38 Selenophene, 2-mercapto-5-methyl-synthesis, 4, 956 tautomerism, 4, 946 Selenophene, 3-methoxy-lithiation, 4, 949, 955 synthesis, 4, 955 Selenophene, methyl-oxidation, 4, 951 synthesis, 4, 963 Selenophene, 2-methyl-lithiation, 4, 949 Selenophene, 3-methyl-synthesis, 4, 963... 

Since 17a-ethynyl-17 -hydroxy steroids are so readily prepared, they represent attractive starting materials for conversion to 20-ketopregnanes. Standard methods for the hydration of aliphatic acetylenes (e.g, mercuric salts alone, with aniline, or with BF3) give variable results, and sometimes no product at all, due to D-homo rearrangement. 233,235,265-7 mercury... 

A rather special procedure for the preparation of 21-hydroxy-20-ketopreg-nanes starts with the 17a-ethoxyethynyl-17 -hydroxy steroids described earlier. Free radical addition of ethanethiol to the triple bond, followed by acid-catalyzed hydrolysis and dehydration gives the 20-thioenol ether 21-aldehyde. This can be reduced with lithium aluminum hydride to the C-21 alcohol and then hydrolyzed to the C-20 ketone in the presence of mercuric chloride. The overall yield, without isolation of intermediates, is in the order of 50% ... 

By Iodine Mercuric Oxide Photolysis of 5a.-Hydroxy Steroids... 

A-Nor-B-homo steroids with different substitution patterns than those described above may be prepared by acid catalyzed cyclization of 3)3-hydroxy-5(10)-seco-cholest-tra/w-l(l0)-en-5-one acetate (134a) formed in 30-40% yield by mercuric oxide-iodine sensitized irradiation of cholestane-3j3,5a-diol... 

Hydroxy-l-alkenyl diisopropylcarbamates 2 (X = OCb), in this respect, occupy a medium position since they are stable in strongly acidic and basic protic solvents. For deblocking vinyl carbamates, the presence of catalytic amounts of mercuric or palladium(II) salts is required. Due to this stability, several reactions of homoallylic alcohols, proceeding with high diastereo-selectivity, e g., epoxidation, are applicable in order to introduce further hetero-substituents. 

This result can be explained in terms of a steric preference for conformation A over B. The approach of the mercuric ion is directed by the hydroxy group. The selectivity increases with the size of the substituent R.25... 

Cyclization induced by mercuric ion is often used in multistep syntheses to form five- and six-membered hetereocyclic rings, as illustrated in Scheme 4.6. The reactions in Entries 1 to 3 involve acyclic reactants that cyclize to give exo-5 products. Entry 4 is an exo-6 cyclization. In Entries 1 and 2, the mercury is removed reductively, but in Entries 3 and 4 a hydroxy group is introduced in the presence of oxygen. Inclusion of triethylboron in the reduction has been found to improve yields (Entry l).113... 

Successful decarboxylations where the substituents favor classic electrophilic aromatic substitution are known. Reaction of 2-hydroxy-l-naphthalenecarboxylic acid with mercuric acetate in cold acetic acid has been reported to give 2-hydroxynaphthalen-l-ylmercuric acetate [Eq. (71)] (84). Although the result probably requires reinvestigation,... 

D. trans-4-Hydroxy-2-hexenal. In a 500-ml., one-necked flask containing a Teflon -coated magnetic stirring bar is placed 3.85 g. (0.02 mole) of l,3-bis(methyIthio)-l-hexen-4-ol, 80 ml. of tetrahydrofuran (Note 11), and 6.00 g. (0.06 mole) of powdered calcium carbonate. The mixture is stirred, and a solution of 16.4 g. (0.06 mole) of mercuric chloride in 140 ml. of tetrahydrofuran and 40 ml. of water is added. The mixture is stirred and heated at 50-55° with a water bath for 15... 

Addition of l,3-bis(methylthio)allyllithium to aldehydes, ketones, and epoxides followed by mercuric ion-promoted hydrolysis furnishes hydroxyalkyl derivatives of acrolein5 that are otherwise available in lower yield by multistep procedures. For example, addition of 1,3-bis-(methylthio)allyllithium to acetone proceeds in 97% yield to give a tertiary alcohol that is hydrolyzed with mercuric chloride and calcium carbonate to saturated aldehyde.8 Similarly, addition of l,3-bis(methylthio)allyl-lithium to an epoxide, acetylation of the hydroxyl group, and hydrolysis with mercuric chloride and calcium carbonate provides a 5-acetoxy-a,/ -unsaturatcd aldehyde,6 as indicated in Table I. Cyclic cis-epoxides give aldehydes in which the acetoxy group is trans to the 3-oxopropenyl group. 

Zinc enolate 4, prepared from acetylene ether pyridine i-oxide, mercuric chloride, and zinc, adds to aldehydes to form a-chloro-3-hydroxy esters 5 in good yields ( ). Subsequent treatment with base gives trans-epoxyesters, one of which 6 is converted to 2-amino-2-deoxy-D-ribose stereoselectively in good yields (O. 

On dehydrogenation with mercuric acetate, matrine, allomatrine, and sophoridine afforded the same dehydro product, 5-hydroxy-6,7-dehydromatrine (180) (196,203). The attachment of a hydroxyl group to C-5 and the double bond in the 6,7 position eliminate differences in the moleeular conformations of 4, 5, and 8. The absence of trans bands in the spectrum of 178 may be explained by isomerization taking place during reduction. 

Nessler s precipitate belongs to the same class of compounds, and may be represented as Hg(QH).NH.HgI, mercuric hydroxy-iodoamide. 

Oxymercuration-reduction of alkenes preparation of alcohols Addition of water to alkenes by oxymercuration-reduction produces alcohols via Markovnikov addition. This addition is similar to the acid-catalysed addition of water. Oxymercuration is regiospecific and auft -stereospecific. In the addition reaction, Hg(OAc) bonds to the less substituted carbon, and the OH to the more substituted carbon of the double bond. For example, propene reacts with mercuric acetate in the presence of an aqueous THF to give a hydroxy-mercurial compound, followed by reduction with sodium borohydride (NaBH4) to yield 2-propanol. 

In spite of the successful implementation of the concept of remote activation of an anomeric 2-pyridylthio group, there emerged various issues and questions. The absence of self-condensation products could be ascribed to the use of excess acceptor in all cases, and possibly to the coordination of the mercuric salt to the free hydroxy groups of the donor, thereby diminishing their reactivity. However, the necessity to use an excess of acceptor (> 5 eq), the formation of anomeric mixtures of glycosides, and the use of a mercuric salt, limited the generality of this method of glycoside synthesis. 

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