Hydration regiospecific

There are two methods for the introduction of a hydroxyalkyl group at position 5 of the pyrazol-3-one ring. Schmidt and Zimmer converted furanediones 258a-k into arylmethylenepyrazol-3-reaction with hydrazine hydrate or methylhydrazine (83Jmechanism proposed for the reaction involves nucleophilic attack of the hydrazine on the ketone carbonyl, followed by attack on the ester carbonyl and ring opening of the... 

Since the addition of HjO to 0=C is Markovnikov regiospecific, RC CH or RC CR must give ketones. Only HC=CH is hydrated to give an aldehyde, CH3CHO. 

Some interesting work has been published dealing with the metal ion-promoted hydrolysis of epoxides. Hanzlik and Michaely499 first observed that in the presence of copper(II) the hydration of 2-pyridyloxirane (153) is accelerated by a factor of 1.8 x 104 and its reaction with Cl-, Br and MeO becomes 100% regiospecific for /3-attack. The magnitude of the catalytic effect decreases in the order Cun> Con>Zn11 Mn". The pH rate profile for the copper(II)-catalyzed reaction is a bell-shaped curve with a maximum at ca. pH 5. 

The hydration of heteroatom-substituted alkynes proceeds well under general acid catalysis. This reaction provides a convenient synthesis of amides,308 esters309 and thioesters.308 Equation (203) illustrates the utility of this reaction for the regiospecific synthesis of 3-alkenamides. 

It is possible to regiospecifically add the hydroxy group to carbon 2 of 1-hexene by using either the oxymercuration reaction or acid-catalyzed hydration. However, it is not possible to selectively add a hydroxy group only to carbon 2 of 2-hexene because both carbons are monosubstituted. Therefore, the path starting from 1-hexene should be used. 

This reaction also provides an attractive route to y-keto esters, since mercuric ion-promoted hydration of, y-acctylcnic c.sters proceeds with regiospecificity 10 give y-keto esters (4). 

The term dihydrodiol is widely used in reference to vicinal dihydroxydihydro-derivatives of aromatic hydrocarbons. Although most known and potential benzene oxide or substituted benzene oxide metabolites tend to be quite unstable, a recent study has described the isolation of a relatively stable arene oxide metabolite of 2,2, 5,5 -tetrachlorobiphenyl. Perhaps because of the generally high susceptibility of benzene oxide 1 and many substituted benzene oxides to isomerize to phenols, relatively little has been reported on the kinetics and regiospecificity of their microsomal epoxide hydrolase (EC 3.3.2.3) catalyzed trans hydration to dihydro-... 

Hydroboration-oxidation, then, converts alkenes into alcohols. Addition is highly regiospecific the preferred product here, however, is exactly opposite to the one formed by oxymercuration-demercuration or by direct acid-catalyzed hydration. For example ... 

Direct amination of 3(2//)-pyridazinones occurs when they are heated with hydrazine hydrate and this is a convenient route to many 4-amino-6-substituted-3(2//)-pyridazinones (Scheme 11). The reaction generally gives high yields and amination is regiospecific when the 6-position is occupied by an aromatic or heteroaromatic ring, but the parent 3(2/ -pyridazinone gives a mixture of the 4- and 5-amino-3(2//)-pyridazinones. The reaction tolerates jV-methyl substitution of the pyridazinone, but is sensitive to steric factors the presence of a 5-substituent causes a marked reduction in reaction rate, and amination does not occur with 4-phenyl-3(2//)-pyridazinone. With maleic hydrazide 4-hydrazination occurs, possibly by displacement of an intermediate amino compound or by oxidation of an intermediate 4,5-dihydro-4-hydrazino adduct both 4-hydrazino- and... 

Patil, M. L., Jnaneshwara, G. K., Sabde, D. R, Dongare, M. K., Sudalai, A., and Deshpande, V. H. 1997. Regiospecific acylations of aromatics and selective reductions of azobenzenes over hydrated zirconia. Tetrahedron Lett., 38 2137-2140. 

A similar reaction between the hydroxyamino enaminones 301 and hydrazine hydrate affords a regiospecific synthesis of 3(5)-alkyl/arylamino-4-nitrosopyrazoles 302 and, under more forcing conditions, 3(5)-alkyl/ arylamino-4-aminopyrazoles 303, Scheme 84 (93JHC129). However, the reactions of enaminones 304 with hydrazines led to the methylthiopyrazoles 305, because the amino group was unexpectedly the leaving group. Scheme 85 (70ACS3109). 

Oxytelluration of olefins with PhTeBrs or Ph2Te2-Br2 in aqueous THF generates (P-hydroxyalkyl)aryltelluiium dihalides. The reaction is tran -stereospecific in the case of cw-2-butene and cis- and trans-4-octenes and regiospecific in the cases of all terminal olefins. Their reactions with reducing agents in aqueous sodium hydroxide generate the Markovnikov hydration products. 

A new approach to the 5-keto-aldehydes frequently employed as spiro-system precursors utilizes the known regiospecific hydration of acetylenic ketones. Thus the acetylenic aldehyde (167), produced by alkylating the t-butylimine (166) with trimethylsilylpropargyl bromide, underwent simultaneous regiospecific hydration and deprotection to (168) on treatment with mercuric sulphate in aqueous THF containing a trace of H2S04. ° ... 

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