Hetero-substituents compounds

Benzyl-type carbanions and their metallo compounds, derived from aromatic or hetero-aromatic precursors, bearing carbon- or hetero-substituents, are readily available with variable substitution patterns due to their mesomeric stabilization (see Section 1.3.2.2)2. Even dicarbanions are accessible without difficulty3,4. The equilibrium acidities of many aromatic hydrocarbons have been determined5-7. The acidities of a-hetero-substituted toluenes8 are similar to those of the corresponding allylic compounds and can usually be generated by the same methods. 

Allyl anion synthons A and C, bearing one or two electronegative hetero-substituents in the y-position are widely used for the combination of the homoenolate (or / -enolate) moiety B or D with carbonyl compounds by means of allylmetal reagents 1 or 4, since hydrolysis of the addition products 2 or 5 leads to 4-hydroxy-substituted aldehydes or ketones 3, or carboxylic acids, respectively. At present, 1-hetero-substituted allylmetal reagents of type 1, rather than 4, offer the widest opportunity for the variation of the substitution pattern and for the control of the different levels of stereoselectivity. The resulting aldehydes of type 3 (R1 = H) are easily oxidized to form carboxylic acids 6 (or their derivatives). 

The diazonium ions 2.13 with electron-withdrawing substituents are not hetero-aromatic compounds and therefore do not strictly come within the scope of this book. They are formally related to the alkenediazonium ions. Nevertheless, they are discussed here because in their properties they bear a close resemblance to heteroaromatic and arenediazonium ions rather than to alkenediazonium ions. In par-... 

Several benzothiazinone analogs have been synthesized in an attempt to introduce hetero substituents at the a-carbon center in these heterocyclic compounds. The required a-halo-benzothiazinone intermediate 148 was prepared by chlorination with sulfiiryl chloride. This material was used successfully in an Arbuzov reaction to prepare the phosphonate diester 149,... 

Since the activity seemed highly dependent on the positions of hetero-atom substituents, the compounds were stereochemically classified into two groups, meso- and (//-analogs, according to their hetero-substituent positions as shown in Fig. 12. QSAR analyses for insecticidal activity of these groups were performed separately to give Eq. 52 and 53 74). 

A higher reaction temperature is necessary when pyrazolones such as 15 and isoxazolones are used. The selectivity in these reactions depends on the substituent at the hetero-aromatic compound and the substituents at the dienophile moiety (Scheme 5.4) [10]. 

Perylenediimides represent another class of photoactive dyes which are characterized by their strong fluorescence emission and facile electrochemical reduction. Recently, a supramolecular bis(phthalocyanine)-perylenediimide hetero-triad (compound 42) has been assembled through axial coordination [47]. Treatment of perylenediimide 43, which has two 4-pyridyl substituents at the imido positions, with 2.5 equiv. of ruthenium(II) phthalocyanine 44 in chloroform affords 42 in 68% yield (Scheme 3). This array shows remarkable stability in solution due to the robustness of the ruthenium-pyridyl bond. Its electronic absorption spectrum is essentially the sum of the spectra of its molecular components 43 and 44 in... 

A number of recent reviews exist about intermolecular and intramolecular reactions of the iV-acyl-iminium intermediate. Moreover, detailed accounts of the application in alkaloid synthesis have recently appeared. This chapter deals with reactions of species (1) with nucleophilic alkenes (and alkynes). Other synthetically useful nucleophiles like aromatic rings, active methylene compounds and organome-tallics will not be discussed here. In (1) R, and R are hydrogen or carbon substituents, and R may also be a hetero substituent, such as alkylamino or alkoxy. This chapter differs from previous reviews, as the material is ordered here on the basis of the structural features of the A -acyliminium intermediate. Major emphasis is placed on recent developments and stereochemical details. 

Moreover, the methylenation of lactones 210 with dimethyltitanocene was examined to synthesize 3-alkylidene-2-methyleneoxetanes 212. The yields of 212 depended strongly on the steric hindrance at C4. Bulkier substituents at C4 led to higher yields, and up to 75% yield was acquired with lactones 210d. Preliminary investigations of the reactivity of these unusual, strained hetero-cycUc compounds have been carried out. Using 212a as a model substrate, several potential applications of such 3-alkylidene-2-methyleneoxetanes as synthetic scaffolds were demonstrated (Scheme 4.64). 

Pd-catalyzed site-selective cross-coupling reactions demonstrate the influential role of ligands in transition metal catalysis. The reactions described in this review discuss efficient approaches to introduce various substituents at specific halo-substituted posititMis (Ml (hetero)aromatic compounds. The commercial availability of a variety of dihalo-substituted starting materials makes site-selective crosscoupling reactions practical for the rapid production of diverse (hetero)arenes with multiple substituents. In all examples described here, the reactions proceeded successfully only on substrates containing hetero atoms, and this field of chemistry aims to include substrates without hetero atoms in the substrate scope. 

A general stereochemical pattern of the aldol addition is shown in Scheme 1.5. When a carbonyl compound 28 with an a-substituent R (which can be an alkyl or an aryl group, or a hetero substituent, for example alkoxy, or a protected amino group, but which is not identical with hydrogen) is converted into the preformed enolate 29 and added to an aldehyde, four ster-eoisomeric products 30a, 30b, 31a, 31b can result. 

Reactions of aromatic and heteroaromatic rings are usually only found with highly reactive compounds containing strongly electron donating substituents or hetero atoms (e.g. phenols, anilines, pyrroles, indoles). Such molecules can be substituted by weak electrophiles, and the reagent of choice in nature as well as in the laboratory is usually a Mannich reagent or... 

The a and y are used to denote the position of a substituent relative to a cyclic hetero atom thus 4-hydroxy isoquinoline is a /3-hydroxy compound. 

Hydroxyalkylation of these allyltitanium derivatives by carbonyl compounds proceeds at the more highly substituted terminus. Exceptions are observed for those hetero-substitutcd derivatives in which the chelating substituent Y ties the cation to the 1-position. 

Reactions of 2,3-dihydro-17/-1,4-diazepines with mesitonitrile oxide proceed with site- and regiospecific 1,3-dipolar cycloaddition leading to bis[ 1,2,4] oxadiazolo[l,4]diazepine derivatives 160 (326). Of the three compounds 160 only the one with R = R = Ph is formed with trails arranged substituents. The two other products (R = R = Me and R = Me, R = Ph) are mixtures of diastereoiso-mers. The heterotricyclic 6,1 Oa, 11,11 a-tetrahydro-5//-bis[ 1,2,4]oxadiazolo[4,5-d 5 -g][, A diiazeipm.e structure 160 of the obtained bis-adducts indicates that the hetero double bonds are much more reactive than the olefinic ones. No evidence for the formation of monoadducts was obtained. 

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