Substituted groups reactions

Stilbene derivative 6b,10b-dihydrobenzo[/]cydobut[a]acenaphthylene (DBCA) was 

In the next step, pleiadene dimerizes. Synthesis of either ( )-3,5-dimethoxystil-benes or 3,5-dimethoxydibenzyls was carried out by selective removal of the 4-methoxy group of 3,4,5-trimethoxystilbenes I (Ri = MeO Ar = Ph, 2-MeOCfiH4, 3-MeOC6H4, 4-MeOC6H4, 3,4,5-(MeO)3C6H2) [75]. The reaction was performed under electron transfer conditions with Na metal in THE. It was shown that 4, 4 -diethylstilbestrol quinone reacted with nucleosides, nucleotides, and amines 

P -postlabeling analysis to bind covalently to DNA in iwo and invitro [79]. Influence of DES dose, age of animals, and organ specificity on adduct formation in hamsters has been examined. The covalent binding of DES to DNA catalyzed by hamster liver microsomes required cumene hydroperoxide as a cofactor. It was su ested that stilbene-DNA adduction may occur only under oxidative stress conditions. 

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The most widely used reactions are those of electrophilic substitution, and under controlled conditions a maximum of three substituting groups, e.g. -NO2 (in the 1,3,5 positions) can be introduced by a nitric acid/sul-phuric acid mixture. Hot cone, sulphuric acid gives sulphonalion whilst halogens and a Lewis acid catalyst allow, e.g., chlorination or brom-ination. Other methods are required for introducing fluorine and iodine atoms. Benzene undergoes the Friedel-Crafts reaction. ... 

Hydroxyl Group. Reactions of the phenohc hydroxyl group iaclude the formation of salts, esters, and ethers. The sodium salt of the hydroxyl group is alkylated readily by an alkyl hahde (WiUiamson ether synthesis). Normally, only alkylation of the hydroxyl is observed. However, phenolate ions are ambident nucleophiles and under certain conditions, ring alkylation can also occur. Proper choice of reaction conditions can produce essentially exclusive substitution. Polar solvents favor formation of the ether nonpolar solvents favor ring substitution. 

The apphcation of bimolecular, nucleophilic substitution (S ) reactions to sucrose sulfonates has led to a number of deoxhalogeno derivatives. Selective displacement reactions of tosyl (79,85), mesyl (86), and tripsyl (84,87) derivatives of sucrose with different nucleophiles have been reported. The order of reactivity of the sulfonate groups in sucrose toward reaction has been found to be 6 > 6 > 4 > 1. ... 

Alkylthio groups are replaced in nucleophilic substitutions. Such reactions are easy in cationic derivatives for example, in the 1,2-dithiolylium series (539), substituted cydopen-tadienyl ion gives fulvene derivatives (540) (66AHC(7)39). 2-Methylthio groups in... 

The second phase in resole formation is reaction of the activated phenol with the aldehyde to form the phenol alcohol derivative. When the aldehyde is formaldehyde, the derivative is a hydroxymethyl phenol and the process is known as methylolation. Scheme 2 illustrates this reaction. Since resoles are usually made with excess aldehyde, more than one substitution may be made on the ring. When the reactants are phenol and formaldehyde, up to three methylol groups may be substituted. This reaction has been extensively studied and the rates of... 

The carboxyl groups of amino acids undergo all the simple reactions common to this functional group. Reaction with ammonia and primary amines yields unsubstituted and substituted amides, respectively (Figure 4.9a,b). Esters... 

Another approach for anchoring the carboxyl groups to the aromatic ring of PS is to use a two-step method [35]. In this method, first, the reaction of PS with 2-chloro-benzoylchloride is carried out. The product can then be followed as shown in Scheme (8). If chloro atom is as o-position on benzoyl chloride the reaction occurred as (a). If there is no substitute group o-position on benzoyl chloride, the preferred is reaction (b). 

The addition of a nucleophile to a polar C=0 bond is the key step in thre< of the four major carbonyl-group reactions. We saw in Chapter 19 that when. nucleophile adds to an aldehyde or ketone, the initially formed tetrahedra intermediate either can be protonated to yield an alcohol or can eliminate th< carbonyl oxygen, leading to a new C=Nu bond. When a nucleophile adds to carboxylic acid derivative, however, a different reaction course is followed. Tin initially formed tetrahedral intermediate eliminates one of the two substituent originally bonded to the carbonyl carbon, leading to a net nucleophilic acy substitution reaction (Figure 21.1. ... 

We ve now studied three of the four general kinds of carbonyl-group reactions and have seen two general kinds of behavior. In nucleophilic addition and nucleophilic acyl substitution reactions, a carbonyl compound behaves as an electrophile. In -substitution reactions, however, a carbonyl compound behaves as a nucleophile when it is converted into its enol or enolate ion. In the carbonyl condensation reaction that we ll study in this chapter, the carbonyl compound behaves both as an electrophile and as a nucleophile. 

Two of the four general carbonyl-group reactions—carbonyl condensations and basic conditions and involve enolate-ion intermediates. Because the experimental conditions for the two reactions... 

Biochemistry is carbonyl chemistiy. Almost all metabolic pathways used by living organisms involve one or more of the four fundamental carbonvl-group reactions we ve seen in Chapters 19 through 23. The digestion and metabolic breakdown of all the major classes of food molecules—fats, carbohydrates, and proteins—take place by nucleophilic addition reactions, nucleophilic acyl substitutions, a substitutions, and carbonyl condensations. Similarly, hormones and other crucial biological molecules are built up from smaller precursors by these same carbonyl-group reactions. 

The retro-Claisen reaction occurs by initial nucleophilic addition of a cysteine -SH group on the enzyme to the keto group of the /3-ketoacyl CoA to yield an alkoxide ion intermediate. Cleavage of the C2-C3 bond then follows, with expulsion of an acetyl CoA enolate ion. Protonation of the enolate ion gives acetyl CoA, and the enzyme-bound acyl group undergoes nucleophilic acyl substitution by reaction with a molecule of coenzyme A. The chain-shortened acyl CoA that results then enters another round of tire /3-oxidation pathway for further degradation. 

When aromatic nitro compounds are treated with cyanide ion, the nitro group is displaced and a carboxyl group enters with cine substitution (p. 854), always ortho to the displaced group, never meta or para. The scope of this reaction, called the von Richter rearrangement, is variable. As with other nucleophilic aromatic substitutions, the reaction gives best results when electron-withdrawing groups are in ortho and para positions, but yields are low, usually < 20% and never > 50%. 

With the ArH ArTlX2 Arl reaction sequence available as a rapid and reliable probe for aromatic thallation, a detailed study was undertaken of the various factors affecting orientation in this electrophilic metallation process (153). The results, which are summarized below, demonstrate that aromatic thallation is subject to an almost unprecedented degree of orientation control coupled with the ease with which thallium can then be displaced by other substitutent groups (this aspect of the synthetic exploitation of aromatic thallation is discussed in detail below), the sequential processes of thallation followed by displacement represent a new and versatile method for aromatic substitution which both rivals and complements the classic Sandmeyer reaction. 

Allyl carbamates also can serve as amino-protecting groups. The allyloxy group is removed by Pd-catalyzed reduction or nucleophilic substitution. These reactions involve formation of the carbamic acid by oxidative addition to the palladium. The allyl-palladium species is reductively cleaved by stannanes,221 phenylsilane,222 formic acid,223 and NaBH4,224 which convert the allyl group to propene. Reagents... 

The directive effect of allylic silyoxy groups has also been examined. The reactions are completely regioselective for 1,3-oxygen substitution. The reaction of... 

The chloro group of 6 is now highly activated toward nucleophilic aromatic substitution, facilitating reaction with phenoxide. Subsequent catalytic reduction in the presence of LiOH produces amino acid 7. Next, treatment with butanol and sulfuric acid not only forms the butyl ester but monoalkylates the amino function. Saponification of the ester group leads to bumetanide (8), a diuretic agent possessing 40-fold greater activity in healthy adults than furosemide. ... 

The final group of threefold anionic domino processes described here includes transformations with an initiating elimination step which is either followed by two Michael additions or by substitutions. Thus, reaction of protected nitro alcohol 2-... 

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