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5-exocydization

The l-methyl-5-hexenyl radical also gives predominantly the ds-product, due to a combination of steric and stereoelectronic factors. 5-exoCydization proceeds with... [Pg.137]

Most of the reactivity studies on 2-aminothiazole and its derivatives are related either to exocydic nitrogen reactivity or to ring nitrogen reactivity. Active species involved in such reactions may depend on the pH. the... [Pg.30]

Left bonded atom linked to exocydic nitrogen right bonded atom linked to ring K. ... [Pg.283]

Left bonded atom linked to exocydic nitrogen right bonded atom linked to ring N. TABLE VI-69, R3 /R2 R, S- NCOR, R, = NRR. OR. SO R. ... [Pg.288]

Migration of an aDaryl group from a heterocyclic to an exocydic N... [Pg.96]

Knolker and coworkers also used a domino [3+2] cycloaddition for the clever formation of a bridged tetracyclic compound 4-172, starting from a cyclopentanone 4-168 and containing two exocydic double bonds in the a-positions (Scheme 4.36) [57]. The reaction of 4-168 with an excess of allylsilane 4-169 in the presence of the Lewis acid TiCLj led to the spiro compound 4-170 in a syn fashion. It follows a Wag-ner-Meerwein rearrangement to give a tertiary carbocation 4-171, which acts as an electrophile in an electrophilic aromatic substitution process. The final step is the... [Pg.303]

Zr-Catalyzed Kinetic Resolution of Exocydic Allylic Ethers... [Pg.191]

Amenate derivatives that do not carry substitutents at the exocydic nitrogen atom undergo a ring-opening reaction to nitroso cyanohydrazines 127 upon treatment with bases in aqueous solutions [151]. [Pg.167]

Amenates acylated at the exocydic nitrogen are stable as solid compounds but decompose in aqueous solutions releasing NO. This decomposition depends on the pH and most importantly on their chemical structure [147, 152]. The proposed mechanism of NO-release is shown in Scheme 6.24. It is related to that postulated for sydnonimines. The main difference is that here 5-substituted amenates 128 are able to react with water to form acyclic nitroso semicarbazides 129 directly without needing enzymatic cleavage, and these intermediates release NO by an oxidative or thiol mediated mechanism that is not fully understood [153]. [Pg.167]

So far, the formation of cyclic alkoxyallenes bearing an exocydic or endocyclic allenyl unit has been less developed. Several examples with this structural feature are described as unstable compounds or highly reactive intermediates [32-35]. However, in the 1990s, Lavoisier-Gallo and Rodriguez demonstrated a useful one-pot protocol for the synthesis of 2-vinylidenedihydrofurans such as 29 involving a tandem C-O cycloalkylation of stabilized carbanion intermediates 28 as crucial step (Scheme 8.10) [36, 37]. [Pg.430]

Details of various routes to allylphosphine oxides (43) have been reported, and the subsequent synthesis of 1,3-dienes has been illustrated by many examples.37 Also described are stereochemical aspects of these diene syntheses and of subsequent Diels-Alder cycloaddition reactions.37 High regioselectivity is observed in migrations of the diphenylphosphinoyl group from unsymmetrical sites, as in (44), in that both products have a double bond exocydic to the cyclohexane ring.38... [Pg.79]

Figure 1.11 provides an example of H NMR monitoring in the Pd-catalyzed cy-doisomerization of dimethyl diallyl malonate, 39 [28]. The kinetic profile reveals a pronounced induction period after which the exocydic alkene 40a is formed predominantly as the kinetic product. A hydropalladation mechanism was proposed on the basis of NMR experiments, and the transient spedes 41, formed by allylpalla-dation of the coordinated diene, could be detected and identified with the help of and labeling. The hydride Pd catalyst, 42, would be generated from 41 by water-promoted P-hydride elimination. The observed induction period is assodated with the formation of the Pd-hydride 42. [Pg.10]

Cyclopentaf/z ][2.2.4]cyclazines (297), which are uncharged since there is an exocydic double bond at the [2.2.4]cyclazine periphery, have been prepared by the two routes shown in Scheme 46 <80JCS(Pl)l324, 79TL3405). Electrophilic substitutions (deuteration, nitration,... [Pg.488]

Metal binding of the N-3 position of either 1-methylthymine or 1-methyluracil monoanion facilitates binding of additional metals through exocydic oxygens of these ligands. [Pg.789]

All bond angles in adamantane are nearly 109.5 ° (see above). Theory170) predicts, therefore, that all carbon bonding orbitals should be nearly pure sp3 hydrids. The situation in norbomane is quite different. Endocyclic bond angles of this molecule are considerably less than 109.5 ° 17 l. The p character of the endocyclic carbon orbitals should be greater than that of the exocydic orbitals170). [Pg.48]

Scheme 26 Pyridine nitrogen nucleophiles in exocydic ring closure... Scheme 26 Pyridine nitrogen nucleophiles in exocydic ring closure...
Tautomerism of the A-2-thiazoline-5-thiones has not been investigated intensively. A recent report shows that 2-phenyithiazo e-5-thiols exist in the thiol form in both polar and nonpolar solvents (563). This behavior is in contrast with that of corresponding thiazolones. Addition reactions involve only the exocydic sulfur atom, and thiazole-5-thiols behave as typical heteroaromatic thiols towards unsaturated systems, giving sulfides (153a) (Scheme 80) (563). [Pg.479]

Benzo[Z>]furans and indoles do not take part in Diels-Alder reactions but 2-vinyl-benzo[Z>]furan and 2- and 3-vinylindoles give adducts involving the exocydic double bond. In contrast, the benzofc]-fused heterocycles function as highly reactive dienes in [4+2] cycloaddition reactions. Thus benzofc ]furan, isoindole (benzofc Jpyrrole) and... [Pg.67]

Reactions with Exocydic or Partially Cyclic Cisoid Dienes 384... [Pg.316]


See other pages where 5-exocydization is mentioned: [Pg.264]    [Pg.388]    [Pg.242]    [Pg.23]    [Pg.1059]    [Pg.1070]    [Pg.190]    [Pg.212]    [Pg.36]    [Pg.264]    [Pg.264]    [Pg.853]    [Pg.60]    [Pg.127]    [Pg.663]    [Pg.347]    [Pg.94]    [Pg.122]    [Pg.418]    [Pg.420]    [Pg.87]    [Pg.87]    [Pg.367]    [Pg.110]   
See also in sourсe #XX -- [ Pg.513 ]




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Alkenes exocydic

Exocydic allylic ethers

Exocydic double bond

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