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Carbenes, hydroxyphenyl

Several other studies concerning tetrazole-containing compounds were leptorted. The 1-bromo-glycosyl cyanide 15 was converted to the tetrazole derivative 16 in 72% yield by treatment with 2 eq LiNs/DMF/S d <96T9121>. Shorter reaction times led to formation of the 1-azido-pyranosyl cyanide. (Hydroxyphenyl) carbenes could be formed by thermal decomposition of the appropriate 5-substituted tetrazoles 17 <96JOC4462>. [Pg.165]

Kinetic analysis shows that the formation of tropone through a hydroxyphenyl-carbene intermediate (which exhibits the lowest activation energy 69.3 kcal/mol) dominates o-QM decomposition process up to 1500 K, with fulvene + CO formation becoming competitive at higher temperatures. In fact, the latter decomposition mode although disfavored by its higher activation enthalpy (75.4 versus 69.3 kcal/mol) becomes competitive due to its more positive activation entropy. [Pg.59]

The p-functionalized 2-hydroxyphenyl isocyanide not only contains the isocyanide and the nucleophile within the same molecule, but both functional groups are also arranged in one plane for an intramolecular nucleophilic attack [176]. This arrangement, in addition to the aromaticity of the five-membered ring obtained after cyclization to the carbene ligand, particularly favors the intramolecular nucleophilic attack. In contrast to 2-hydroxyethyl isocyanide, free 2-hydroxyphenyl isocyanide is not stable [177]. The stable 2-trimethylsiloxyphenyl isocyanide [178] can serve as a synthon for 2-hydroxyphenyl isocyanide. Carbene complexes 63 with an NH,0-stabilized NHC ligand can be obtained from the complexes 62 with the... [Pg.115]

Benzene derivatives such as m-methylanisole (40) can be converted to distonic carbene ions. Reaction of 40 with O occurs with loss of H2, generating the conventional carbene anion 41 this anion reacts with molecular fluorine by dissociative ET, followed by nucleophilic attack of F on the methyl group, forming 42. In contrast to phenyhnethylene, 42 has a singlet ground state however, upon protonation it gives rise to the triplet state of m-hydroxyphenyl-methylene. This interesting reaction can be viewed as a spin-forbidden proton-transfer reaction. [Pg.233]

Carbenes on sites adjacent to the phenolic gronp have also been generated. Thns, 2-hydroxyphenyl carbene 170 has been obtained by the pathway shown in Scheme 21. The carbene reacts with the hydroxy group to afford the oxetene (171). This itself is photochemicaUy labile and undergoes ring opening to a quinonemethide . [Pg.1059]


See other pages where Carbenes, hydroxyphenyl is mentioned: [Pg.178]    [Pg.258]    [Pg.306]   
See also in sourсe #XX -- [ Pg.96 , Pg.138 , Pg.384 ]




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4-hydroxyphenyl

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