Regioisomeric forms

For the ABBB monomer, two diastereoisomeric chiral capsules were possible, with a diastereoisomeric ratio that varies from 6 1 in cyclohexane-di2 to 1 1 in chloroform-d, with a strong solvent effect the latter was also the guest and therefore influenced the stability of the capsules both from the inside and outside of the capsule. The ABAB monomer gave rise to only one chiral racemic capsule, while for AABB two regioisomeric structures were possible, with a relative amount from 1 1 to 2 1 increasing the steric difference between A and B from n-hexyl to adamantyl residues. Moreover, the equilibrium between the regioisomeric forms could be shifted entirely on one side if two adjacent A and two B groups are covalently connected. 

Finally, this strategy will be perfectly suited for syntheses of the different possible stereo- and regioisomeric forms of the related, hydroxymethylated alkaloid triphyopeltine (27) (see Section III). 

Schuyl et al (1995) have reported an on-line combination of AgN03 HPLC with ES/MS. Mass spectra of TGs exhibited only abundant [M + Na]" ions without any information on fatty acid moieties. Laakso and Voutilainen (1996) used AgN03-HPLC in combination with on-line APCI/MS for the examination of TGs of seed oils rich in a and/or y-linolenic acid moieties. Mass spectra of most TGs exhibited abundant [M -h H] and [M - RCOO]" ions, which defined the molecular weight and the molecular association of fatty acyl residues of a TG, respectively. Regioisomeric forms of TGs were not determined from the seed oil samples, although differences were measured with reference compounds for the relative abundances of [M - RCOO] ions formed by a loss of a fatty acyl residue from the sn 2 position and the snA A positions. AgN03-HPLC/APCI/MS provided... 

Like fluorene, the three methylene moieties in sumanene can undergo alkylation or aldol condensation (Scheme 38). In the presence of a mixture of aqueous NaOH and Bu4NBr, the reaction of 2 with allyl bromide or 4-methoxybenzyl chloride gave the corresponding hexa-alkylated sumanenes 118 [137]. Similarly, aldehydes yielded 119 in two regioisomeric forms [138]. 

This reaction data set of 626 reactions was used as a training data set to produce a knowledge base. Before this data set is used as input to a neural Kohonen network, each reaction must be coded in the form of a vector characterizing the reaction event. Six physicochemical effects were calculated for each of five bonds at the reaction center of the starting materials by the PETRA (see Section 7.1.4) program system. As shown in Figure 10,3-3 with an example, the physicochemical effects of the two regioisomeric products arc different. 

Another preparative method for the enone 554 is the reaction of the enol acetate 553 with allyl methyl carbonate using a bimetallic catalyst of Pd and Tin methoxide[354,358]. The enone formation is competitive with the allylation reaction (see Section 2.4.1). MeCN as a solvent and a low Pd to ligand ratio favor enone formation. Two regioisomeric steroidal dienones, 558 and 559, are prepared regioselectively from the respective dienol acetates 556 and 557 formed from the steroidal a, /3-unsaturated ketone 555. Enone formation from both silyl enol ethers and enol acetates proceeds via 7r-allylpalladium enolates as common intermediates. 

Both resonance forms of the allylic carbocation from 1 3 cyclopentadiene are equivalent and so attack at either of the carbons that share the positive charge gives the same product 3 chlorocyclopentene This is not the case with 1 3 butadiene and so hydrogen halides add to 1 3 butadiene to give a mixture of two regioisomeric allylic halides For the case of electrophilic addition of hydrogen bromide at -80°C... 

The addition of benzyl azide to monosubstituted diacetylenes initially proceeds at the terminal acetylene bond to form two regioisomeric 4- and 5-ethynyl-1,2,3-triazoles 98 and 99 along with minor amounts of the corresponding diadducts (81ZOR741 82ZOR1619). 

From reaction of an unsymmetrically substituted diene 11a, b and dienophile 12, different regioisomeric products 13a, b and 14a, b can be formed. The so-called ortho and the para isomer 13a, resp. 13b, is formed preferentially. 

With an unsymmetrical ketone as CH-acidic substrate, two regioisomeric products can be formed. A regioselective reaction may in such cases be achieved by employing a preformed iminium salt instead of formaldehyde and ammonia. An iminium salt reagent—the Eschenmoser salt—has also found application in Mannich reactions. ... 

From reaction of simple alkynes and alkenes four regioisomeric products 7a-d may be formed ... 

Usually, isolated C=C double bonds do not react with suifinic acids or their salts to form sulfones. Exceptions represent the chloropalladiosulfonylation of dicyclopen-tadiene and the sulfonylmercuration of 1-alkenes (equation 16). Interestingly, the corresponding iodosulfonylation yields the regioisomeric sulfone . Further investigations concerning the mechanism of this second reaction which could involve the addition of intermediately formed tosyl iodide (rf. Section III.B.l) are announced. 

Deprotonation of the corresponding carbonyl compound is a fundamental method for the generation of enolates, and we discuss it here for ketones and esters. An unsymmetrical dialkyl ketone can form two regioisomeric enolates on deprotonation. 

Carbonylation reactions have been observed using both Pd(II)-alkene complexes and CT-bonded Pd(II) species formed by oxidative addition. Under reductive conditions, the double bond can be hydrocarbonylated, resulting in the formation of a carboxylic acid or ester.238 In nucleophilic solvents, the intermediate formed by solvopalladation is intercepted by carbonylation and addition of nucleophilic solvent. In both types of reactions, regioisomeric products are possible. 

The nitrone and the substituted methylenecyclopropane approach, in each of the two possible regioisomeric arrays, away from the nitrone substituent and away from the methylenecyclopropane substituent. The most favoured anti-anti Transition State produces the observed major diastereoisomers [81,65c]. The only two isomers formed, for each regioisomeric mode, must derive from anti-anti exo and anti-anti endo approaches. No exo-endo selectivity is generally observed, as a consequence of the strong preference for the anti approach towards the substituent on the cyclopropyl ring. 

Triazole derivatives are very interesting compounds that can be prepared by 1,3-dipolar cycloadditions between azides and alkynes. Loupy and Palacios reported that electron-deficient acetylenes react with azidoethylphosphonate 209 to form the regioisomeric substituted 1,2,3-triazoles 210 and 211 under microwaves in solvent-free conditions (Scheme 9.65) [114]. This procedure avoids the harsh reaction conditions associated with thermal cycloadditions (toluene under reflux) and the very long reaction times. 

Acyl azides 268, derived from furan, thiophene and selenophene, add slowly at room temperature to the strained double bond of 5-methylenebicyclo[2.2.1]hept-2-ene. Two regioisomeric triazolines, 269 and 270, which form in the first step, are unstable and decompose with elimination of nitrogen to provide aziridine derivatives 271. Products 271 are isolated in good yield (73-85%). It is worthy to note that not only the terminal, unstrained double bond in the starting material, 5-methylenebicyclo[2.2.1]hept-2-ene, is unaffected, but also the typical dipolarophiles like esters of crotonic, propiolic and byt-2-ynoic acids do not react with azides 268 under these conditions (Scheme 39) <2002J(P1)1420>. 

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