Beta substitutions groups

In contrast to 1, the related pure host 7 may be obtained in crystalline form 68). The crystal structure of 7 is built via helical chains of alternating intra- and inter-molecular H-bonding through the carboxyl functions. This structure supplies the information that the carboxyl groups are therefore already positioned in an appropriate way to facilitate analogous H-bonding in the known inclusions of 7. As discussed later (Sect. 4.2.2), these are exclusively salt-type associates and as such, intimately interact with the carboxyl groups. Hence one may infer that displacement of the carboxyl functions from position 2 in 1 to position 8 in 7 reduces the ability of inclusion formation. Similar reasons such as the solid-solubility differences observed in the classical naphthalene/chloronaphthalene systems (alpha- vs. beta-substituted derivatives, cf. Ref. 28 may also be applied here. 

This acid is closely related to the preceding one. It is hydroxy-phenyl alanine, the group (—C6H4OH) being substituted in the beta carbon group of alanine. Tyrosine is of especial interest as it was one of the first amino acids to be obtained from proteins. It can be easily obtained from cheese. 

This is an amino acid the name of which does not have the ine termination. The beta carbon group in alanine has substituted in it the complex group, (CsHeN), which Is known as the indol radical. Indol is a benzene derivative related to indigo. Tryptophane derives its name... 

This is another amino acid containing a cyclic radical substituted in the beta carbon group of alanine. 

JK Kim, MC Findlay WG Henderson, MC Caserio. Ion cyclotron resonance spectroscopy Neighbouring group effects in the gas-phase ionization of beta-substituted alcohols. J Am Chem Soc 95 2184—2193, 1973. 

Rates of elimination of substrates possessing suitably substituted alpha or beta phenyl groups can be correlated by the Hammett equation " , viz. 

This compound is heated with caustic potash solution, yielding beta-hydroxy-coumarin. From this body, coumarin is obtained by substituting a halogen atom for the OH group, and then reducing the product in alcoholic solution with zinc-dust. 

Beside thioamides, dithioesters are the most stable and accessible thiocarbonyl compounds. Their specific reactivity, in particular towards nucleophiUc reagents and their apphcations to the formation of carbon-carbon bonds, have already been reviewed [8]. However, as shown below, the presence of a phosphonate function alpha or beta to the thiocarbonyl group in phosphonodithioformates and phosphonodithioacetates makes these difunctional compounds very versatile building blocks. Moreover, for the phosphonodithioacetates, the substitution of the methylenic hydrogen atoms by fluorine increases again their potential as intermediates for the synthesis of modified natural and bioactive phosphorylated structures. 

In a substitution reaction, the leaving group is replaced with a nucleophile. In an elimination reaction, a beta ((3) proton is removed together with the leaving group, forming a double bond. In the previous chapter, we saw two mechanisms for substitution reactions (SnI and Sn2). In a similar way, we will now explore two mechanisms for elimination reactions, called El and E2. Let s begin with the E2 mechanism. 

As Table 2 indicates, ligand 23c proved effective for substrates with large, branched groups on the beta positions. The best selectivity was obtained for 54c, which was substituted with aromatic groups on both sides of the substrate, and a large branched alkyl attached to the p position [62]. Entries 54e and 54f are encouraging and may indicate that this method could be extended to more broadly useful compounds. The investigators performed a solvent study and determined the reaction to be equally selective in toluene and dichloromethane so the former was used presumably for its industrial attractiveness. 

Preparation of cyclodextrin derivatives substitution at a secondary hydroxyl group of the cyclodextrin annulus. Murakami and cowor-kers described a new and convenient method for the regioselective tosylation of the 2-hydroxyl groups of alpha, beta, and gamma cyclodextrin by means of a cyclic tin intermediate. The method is based on the reaction of dibutyltin oxide with 1,2-diols to form five-membered dibutyl-stannylidene derivatives. Useful yields of the 2-6>-tosyl derivatives of the cyclodextrins were obtained. 

Chemical structures of several glucocorticoids. The acetonide-substituted derivatives (eg, triamcinolone acetonide) have increased surface activity and are useful in dermatology. Dexamethasone is identical to betamethasone except for the configuration of the methyl group at C16 in betamethasone it is beta (projecting up from the plane of the rings) in dexamethasone it is alpha. 

Olefinic compounds will often insert into carbon-transition metal bonds as CO does, and this reaction is an important step in many catalytic syntheses. When this step is combined with an oxidative addition of an organic halide to a palladium(O) complex in the presence of a base, a very useful, catalytic olefinic substitution reaction results (26-29). The oxidative addition produces an organopalladium(II) halide, which then adds 1,2 to the olefinic reactant (insertion reaction). The adduct is unstable if there are hydrogens beta to the palladium group and elimination of a hydridopalladium salt occurs, forming a substituted olefinic product. The hydridopalladium salt then reforms the... 

The formation of 5-hexenal (reaction 18) is believed to be an intramolecular rearrangement since the addition of oxygen does not cause its suppression. At least in a methyl substituted cyclohexanone the analogous process has been shown to occur by the transfer of a hydrogen atom from the beta position to the carbonyl group before the fission of the six-membered carbocyclic ring (29) as only one of the two possible isomeric heptenals is formed. 

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