Hydroxylation carbons

Hydroxylation, the addition of two hydroxyl groups across a double bond, converts fluonnated alkenes to different products depending on the presence or absence of a fluorine atom at the hydroxylated carbon... 

Reaction of Grignard reagents with esters (Section 14.10) Tertiary alcohols in which two of the substituents on the hydroxyl carbon are the same may be prepared by the reaction of an ester with two equivalents of a Grignard reagent. 

The reaction of hydroxyethyl-TPP with the oxidized form of lipoic acid yields the energy-rich thiol ester of reduced lipoic acid and results in oxidation of the hydroxyl-carbon of the two-carbon substrate unit (c). This is followed by nucleophilic attack by coenzyme A on the carbonyl-carbon (a characteristic feature of CoA chemistry). The result is transfer of the acetyl group from lipoic acid to CoA. The subsequent oxidation of lipoic acid is catalyzed by the FAD-dependent dihydrolipoyl dehydrogenase and NAD is reduced. 

The fact that we can draw a reasonable formula for a molecule is no guarantee that it will be stable. Consider an alcohol that contains a good leaving group attached to the hydroxyl carbon. The alcohol s formula looks reasonable, but the molecule may still spontaneously fragment into HX and the corresponding aldehyde. 

All the oxidants convert primary and secondary alcohols to aldehydes and ketones respectively, albeit with a great range of velocities. Co(III) attacks even tertiary alcohols readily but the other oxidants generally require the presence of a hydrogen atom on the hydroxylated carbon atom. Spectroscopic evidence indicates the formation of complexes between oxidant and substrate in some instances and this is supported by the frequence occurrence of Michaelis-Menten kinetics. Carbon-carbon bond fission occurs in certain cases. 

They indicated that the softness parameter may reasonably be considered as a quantitative measure of the softness of metal ions and is consistent with the HSAB principle by Pearson (1963, 1968). Wood et al. (1987) have shown experimentally that the relative solubilities of the metals in H20-NaCl-C02 solutions from 200°C to 350°C are consistent with the HSAB principle in chloride-poor solutions, the soft ions Au" " and Ag+ prefer to combine with the soft bisulfide ligand the borderline ions Fe +, Zn +, Pb +, Sb + and Bi- + prefer water, hydroxyl, carbonate or bicarbonate ligands, and the extremely hard Mo + bonds only to the hard anions OH and. Tables 1.23 and 1.24 show the classification of metals and ligands according to the HSAB principle of Ahrland et al. (1958), Pearson (1963, 1968) (Table 1.23) and softness parameter of Yamada and Tanaka (1975) (Table 1.24). Compari.son of Table 1.22 with Tables 1.23 and 1.24 makes it evident that the metals associated with the gold-silver deposits have a relatively soft character, whereas those associated with the base-metal deposits have a relatively hard (or borderline) character. For example, metals that tend to form hard acids (Mn +, Ga +, In- +, Fe +, Sn " ", MoO +, WO " ", CO2) and borderline acids (Fe +, Zn +, Pb +, Sb +) are enriched in the base-metal deposits, whereas metals that tend to form soft acids... 

The principal abiotic processes affecting americium in water is the precipitation and complex formation. In natural waters, americium solubility is limited by the formation of hydroxyl-carbonate (AmOHC03) precipitates. Solubility is unaffected by redox condition. Increased solubility at higher temperatures may be relevant in the environment of radionuclide repositories. In environmental waters, americium occurs in the +3 oxidation state oxidation-reduction reactions are not significant (Toran 1994). 

PHA synthases exhibit a remarkably low substrate specificity. In general, the specificity of PHA synthases regarding the length of the hydroxyalkyl moiety of the coenzyme A thioester as well as of the position of the hydroxyl group, the presence of other substituents, and the position of double bonds, is low. In contrast, the stereospecificity of PHA synthases is strict the hydroxyl carbon atom must have the R-configuration. 

Crystallization of the amorphous layer by incorporation of OH-, C032- or F- anions from solution to form a mixed hydroxyl carbonate fluorapatite layer (CHA). 

A magnesium enolate of 99 is susceptible to aldol condensation with 4-pentenal, and the crude product can be directly protected to give its ethyl carbonate 100. a-Hydroxylation of the carbonyl group yields the hydroxyl carbonate 101. Reduction of the carbonyl group generates a triol, and this compound can be simultaneously converted to carbonate 102. Swern oxidation of 102 gives ketone 103, which can be rearranged25 to produce lactone product 104 (Scheme 7-32). 

Direct labelling with deuterium is another approach, and three promising methods have been reported. One, described by Koch and Stuart and coworkers,41 is based on the specific exchange of hydrogen attached to hydroxylated carbon atoms by deuterium atoms that occurs on treatment with Raney nickel-D20. Although no exchange was observed with soluble starch or glycogen, the H-2, H-3, and H-6 atoms of... 

Asymmetric hydroboration.1 Hydroboration of phenyl-substituted trisubstituted alkenes, cyclic or acyclic, followed by oxidation results in alcohols with an optical purity of 80 100%, with the (S)-configuration at the hydroxylaled carbon predominating with reagent prepared from (+)-oc-pinene. 

Reduction of the carbonyl in the r >[CO-CH2-NH] link 7 (R1 = H) results in the (hy-droxy)ethyleneamino or r >[CH(OH)-CH2-NH] link 8 (R1 = H), which has proved to be a very potent analogue of the tetrahedral hydrated intermediate of the scissile amide bond. It has been widely used for the design of various inhibitors of HIV protease 141,142 14 154 and ACE, 155-157 and to synthesize angiotensin II, III, and IV analogues. 158,159 Indeed, the chirality of the hydroxylated carbon is critical for HIV protease inhibition, but separation of the epimers may be difficult. Therefore, the stereoselective synthesis from epoxides has been actively investigated. An example of a C-methylated tp[CMe(OH)-CH2-NH] link, obtained from an epoxide with chromatographic separation of the epimers, has also been described. 157 Most of the [(hydroxy)ethyleneamino] peptides have been prepared by solution procedures, but two examples of solid-phase synthesis have been reported. A theoretical study of the (hydroxy)ethyleneamino replacement for the amide bond has been carried out on a HIV protease inhibitor. 160 ... 

Compounds containing the (hydroxy)ethyleneamino link 8 were originally prepared in solution by reduction with NaBH4 of the carbonyl in the oxomethyleneamino link 7. 141,155,156 This reaction was later adapted to solid-phase conditions. 150,159 Two diastereomers, differing in the chirality of the hydroxylated carbon, have been characterized and their absolute configuration assigned by X-ray diffraction in some cases, 149156 but their separation is usually not possible. 142 ... 

Dihydroxylation, the addition of two hydroxy groups across a C = C bond, converts fluorinated alkenes into different products depending on the presence or absence of a fluorine atom at the hydroxylated carbon. Partially fluorinated alkenes with vicinal hydrogen atoms attached to the C = C bond can be hydroxylated to vicinal diols. When the reaction is performed with a sufficiently strong oxidizing agent, the initially formed diols are oxidized to vicinal diketones as the end products. 

Unlike the reactions discussed previously in this chapter, oxidation of alcohols involves the alkyl portion of the molecule, or more specifically, the C-H bonds of the hydroxyl-bearing carbon (the a carbon). Secondary alcohols, which have only one such C-H bond, are oxidized to ketones, whereas tertiary alcohols, which have no C-H bonds to the hydroxylic carbon, are oxidized only with accompanying degradation into smaller fragments by cleavage of carbon-carbon bonds. 

Hydroxylation of alkanes preferentially occurs at the more nucleophilic C—H bonds, with a relatively low isotope effect (fcH/fcD = 2.8 for cyclohexane) and a significant amount of epimerization at the hydroxylated carbon atom. Radical carbon intermediates were revealed in this reaction by trapping experiments with chlorine atoms coming from CC14. 

Alkanes are preferentially hydroxylated at the more nucleophilic C—H bonds, with relative reactivities tertiary secondary primary hydrogens = 7000 110 l.303 This reaction occurs with a high retention of configuration at the hydroxylated carbon atom, as shown by the selective formation of cis-9-decalol from the oxidation of cis-decalin with chromyl acetate in an acidic medium304 and the hydroxylation of chiral (+)-3-methylheptane (91) to chiral alcohol (92) with 72 to 85% retention of configuration.305... 

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