Substitution hydroxyl substituents

Table 3 gives the corresponding physical properties of some commercially important substituted pyridines having halogen, carboxyHc acid, ester, carboxamide, nitrile, carbiaol, aminomethyl, amino, thiol, and hydroxyl substituents. 

Aromatic rings are hydrogenated with a variety of catalysts. However, aromatic alkoxy and hydroxyl substituents are susceptible to hydrogenolysis under most conditions used to saturate the ring. Hydrogenolysis does not occur to any appreciable extent with ruthenium catalysts even though high temperatures and pressures are required. Thus, substituted phenols are... 

The cholestane molecule may have hydroxyl groups substituted at 25 of its 27 carbon atoms (C-10 and C-13 excepted). Each of these carbon atoms is so situated that it renders its hydroxyl substituent(s) sterically and, more subtly, electronically unique with respect to each of the others. If the cholestane skeleton is maintained, each of the possible secondaiy hydroxyls may assume... 

An old nfflne for benzene was phene, and its hydroxyl derivative cane to be called phenol This, like many other entrenched common nfflnes, is an acceptable lUPAC name. Likewise, o-, m-, and p-cresol are acceptable nanes for the various ring-substituted hydroxyl derivatives of toluene. More highly substituted compounds are named as derivatives of phenol. Numbering of the ring begins at the hydroxyl-substituted carbon and proceeds in the direction that gives the lower number to the next substituted carbon. Substituents are cited in alphabetical order. 

Figure 13.10.2 The structure of a beta hydroxy acid, a substituted carboxylic acid in which the hydroxyl substituent is attached to the beta position, i.e., at a carbon atom two positions away from the carboxylic acid functionality.

Enantioselective Diels-Alder reactions of acrolein are also catalyzed by 3-(2-hydroxy-3-phenyl) derivatives of BINOL in the presence of an aromatic boronic acid. The optimum boronic acid is 3,5-di(trifluoromethyl)benzeneboronic acid, with which >95% e.e. can be achieved. The transition state is believed to involve Lewis acid complexation of the boronic acid at the carbonyl oxygen and hydrogen bonding with the hydroxyl substituent. In this transition state, re,re-interactions between the dienophile and the hydroxybiphenyl substituted can also help to align the dienophile.65... 

It was shown that the protonation regioselectivity was strongly controlled by methoxy and hydroxyl substituents, whose directive effects overwhelmed the methyl substitution effects." Regiocontrol by —OMe and —OH substituents, and its stronger influence relative to methyl groups, was also observed in the nitration and bromination reactions (Fig. 21). Regioselectivities observed in the nitration and bromination reactions in representative cases were the same as those via protonations. 

Methyl substituents in 3,4 -bipyridines have been oxidized by permanganate to the corresponding carboxylic acids, which are readily decar-boxylated, and esters have been converted to amides. 3,4 -Bipyridine-3 -sulfonic acid on fusion with potassium ferricyanide affords 3 -cyano-3,4 -bipyridine. Cyano-substituted 3,4 -bipyridines have been hydrolyzed to the amide or carboxylic acid, " and the amides were converted to amino groups. Hydroxyl substituents in the 2, 6, 6-positions of 3,4 -bipyridine have been replaced by chloro groups with phosphorus... 

A series of studies have been reported on the basicities and nucleo-philicities of 4-substituted and 4,4 -disubstituted piperidines, together with related work on decahydroquinolines.211-215 Substituent effects on pKa values determined in methanol of 4,4 -disubstituted A-methyl-piperidines216,217 and 1,2,5-trimethylpiperidines (25)218 were found to be dependent on o i.e., as expected, resonance effects are absent, the hydroxyl substituent where present taking the axial conformation (24),216 owing to a bridging molecule of methanol. 

In the context of the development of enzymatic methods for the synthesis of higher-carbon sugars we recently developed a new strategy by which dodeca-2,11-diuloses — formally derived from ketohexoses by C-coupling tail to tail — become accessible with deliberately addressable substitution patterns by the twofold aldolase-catalyzed chain elongation ( tandem aldolization) of simple, readily available dialdehydes [207]. The choice of furanoid (179) or pyranoid (180) nature of the products can be determined by a suitable placement of hydroxyl substituents in the allylic (181) or homoallylic ( 182) positions of a corresponding cycloolefinic precursor. 

In p-chlorophenol the benzene ring bears a chlorine and a hydroxyl substituent in a 1,4-substitution pattern. 

Chemical modification of both the primary and secondary hydroxyl substituents has been used to further improve their toxicity, water solubility, and biodegradability. Since the hydroxyl groups differ in chemical reactivity, chemical modification typically produces thousands of regio- and stereoisomers resulting in a substantially less crystalline molecule. The amorphous character of chemically modified cyclodextrins has beneficial effects on aqueous solubility and toxicity. Variation of the degree of substitution provides a means for optimizing physical and chemical parameters of the molecules in specific applications. 

The same authors studied the stereodynamics of some 6-substituted 3-hydroxy-1,3-oxazinanes 137 (cf. Scheme 50) (99SA(A)1445) the composition of the conformational equilibria and the barriers to N-inversion are shown in Table XVIII. Again the conformer with an axially disposed hydroxyl substituent was found to be preferred (cf. Scheme 50), the minor conformer was the di-equatorial invertomer after N-inversion. The axial preferences of the R-N-C-0 units are due to hyperconjugation (97JOC6144). 

In one of the last transformations in a multistep synthesis of 1,2-dihydro-8-ep/-vernolepin (43), nucleophilic intramolecular substitution at an iodomethyl group was promoted by heating an ester precursor with an equivalent of NaOAc in DMF (Equation (18)) <95TL3ii>. Molecular mechanics analysis of the precursor produced a minimum energy conformer that showed the hydroxyl substituent too distant from the iodomethyl group to have interfered with this high yield transformation. 

The details of the reaction conditions used in this study have been described elsewhere (Dershem, S. M., et al., Holzforschung Fisher, T. H., et al., J. Org. CAem., in press). To test the importance of a p-hydroxyl substituent, the kinetics of oxidation of three benzyl alcohols p-hydroxybenzyl alcohol, (1), m-hydroxybenzyl alcohol, (2), and 4-hydroxy-3-methoxybenzyl alcohol, (3), were examined under alkaline nitrobenzene oxidation conditions. Some l-(4-hydroxyphenyl)-2-(4 -substituted phenyl)ethanols, (4), were synthesized as / -l lignin model compounds and subjected to alkaline nitrobenzene oxidation at 120 °C to study substituent effects. For controls, some of these compounds were reacted with or without nitrobenzene, alkaline catalyst, or water. In an effort to determine the effects of substituents on the oxidative-cleavage reaction of 4-hydroxystilbenes (5), a series of competitive rate experiments using both nitrobenzene and copper(II) as the oxidants in 2N NaOH was performed (Dershem, S. M., et al., Holzforschung, in press). 

The stereochemistry uf the tetracyclines is very complex. Carbon atoms 4. 4a.. S.. Na. 6. and 12a arc potentially chiral, depending on substitution. Oxytctracyclinc and doxycyclinc. each with a Sa-hydroxyl substituent, have six asymmetric centers the others, lacking chirality at C-. >. have only five. Determination of the complete, absolute stcreochemi.stry of the tetracyclines w.as a difficult problem. Detailed x-ray diffraction analysis c.siablished the stereochemical formula shown in Table 10-6 as the orientations found in the natural and semisynthetic tetracyclines. Tlic.se studies also confirmed that conjugated systems exist in the structure from C-10 through C-12 and from C-1 through C-.T and that the formula represents only one uf. several canonical forms exi.st-ing in those portions of the molecule. 

Acid mediated elimination of cyclic (dienyl ether)- and (dienol)Fe(CO)2L complexes leads to the formation of (cyclodienyl)Fe(CO)2L cations (equation 26 and 27) . Protonation of (pentadienol)- or (pentadienyl ether)Fe(CO)3 complexes generates the corresponding (pentadienyl)Fe(CO)3+ cations 167 (Scheme 41). Lillya and coworkers have demonstrated that ionization of the hydroxyl substituent occurs with anchimeric assistance from iron, and that isomerization of the initially generated transoid pentadienyl cation 168 to the more stable cisoid cation occurs with retention of configuration about the Cl—C2 bond . The in situ generated transoid pentadienyl cations may also undergo reaction with heteroatom, hydride or carbon nucleophiles to afford substituted ( , -diene)Fe(CO)3 products (169) . Acyclic (pcntadicnyl)MCp cations (M = Rh, Ir) may be prepared by acidic dehydration of (dienol)MCp complexes. ... 

Fig. 11.1 General structure of cellulose with three possible substitution sites indicated by R (not aU are substituted) (hydroxyl groups) on each D-anhydroglucose monomer. Hydroxypropyl meth-ylceUulose (HPMC) contains methoxyl (CHj-O) and hydroxypropoxyl (CH CHOHCH -O) substituents...

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