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Gold carbene direct

The largest l, -enyne that has been cyclized is a 1,9-enyne, which forms a 10-membered ring in the presence of a large amount of gold and silver complex (Scheme 1.26) [200]. The cycloisomerization presumably occurs via cyclopropyl gold carbene XXXVI, which can open to carbocation XXXVII or give directly the 10-membered ring. [Pg.21]

DFT calculations have been carried out to shed some light on the mechanism for cyclobutene formation. No direct pathway for the formation of cyclobutene 11-14 from flnf/-exo-cyclopropyl gold carbene 11-13 was found (Scheme 3.9). In contrast, iyw-exo-cyclopropyl gold carbene 11-13 forms cyclobutene 11-14 by a cyclopropane ring expansion. The formation of iyn-exo-cyclopropyl gold carbene 11-13 has been postulated to occur by a iyn-type attack of the alkene to the alkyne gold moiety in 11-15. However the anti attack is more favorable the syn attack could compete if the substitution at the alkene and/or the alkyne does not favor the skeletal rearrangement [Ref. 15 in Chap. 1]. [Pg.64]

The gold(I)-catalysed rearrangement of cyclopropenes has been explored by DFT calculations, which indicate that the product ratio is controlled by the initial formation of a gold carbene intermediate by substituent-directed cyclopropene ring opening. " ... [Pg.194]

Direct reaction of the bis(isonitrile)gold(I) cations with alcohols or amines also gave the biscarbene complexes [Eq. (38)] (132, 141, 142). With bulky C6HnNC, only one carbene moiety was formed (141, 142) under the conditions employed in the preparation of the other biscarbene compounds. [Pg.59]

The process has been expanded to the synthesis of gold and palladium complexes by Furst and Cazin [99]. Indeed, different neutral copper complexes efficiently transferred their carbenes to gold(I) and palladium(II) (Scheme 8.40). Dichloromethane seemed to be the best solvent under mild conditions (40 °C). Several carbenes were tested to rationalize the ligand effect. When less hindered IMes and SIMes were used, the reaction proceeded smoothly in only Ih, whereas IPr required almost 2h to reach completion. [Cu(Cl)(SIPr)] does not allow the transmetalation to occur and only decomposition was observed. The hindrance of the carbene ligands directly affects the transfer the more hindered the system, the less efficient the transmetalation. [Pg.260]

Furthermore, it has to be emphasized that this method allows straightforward access to gold complexes carrying unsymmetrically substituted NHC ligands. Apart from this it has to be noted that NHC derivates, which bear CH-acidic protons (the NHOC and eNHC systems) that can potentially lead to problems during the formation of the carbene/attachment to the metal center, can be synthesized easily and under mild conditions. Due the fact that m the NHOC systems an enolization can directly Influence the electronic situation at the carbene carbon atom, these systems are also called switchable carbenes. ... [Pg.271]

The mechanism for this reaction is analogous to its intramolecular version [Ref. 223 in Chap. 1], and starts with the formation of the cyclopropyl carbene I-ll (Scheme 2.6). Direct attack of the aldehyde to the cyclopropyl gold(I) intermediate 1-11 leads to the oxonium cation 1-20, which suffers Prins-type cycUzation to give tetrahydropyranyl cation 1-21. Intermediate 1-21 can undergo metalation to yield bicycle 1-16 or can evolve by a fragmentation reaction to form 1,3-diene 1-17. [Pg.41]

As a versatile alternative to the generation of free carbenes, Hashmi and co-workers developed a methodology for the synthesis of abnormal NHCs where the carbene is constructed directly at the metal center. Thus, a [3 + 2] dipolar cycloaddition of azomethine ylides and gold isonitriles afforded the abnormal saturated imidazolinylidene gold eomplexes 9 [eqn (3.3)]. This methodology circumvents the regioseleetivity issue of C4 vs. C5 eoordination because the carbenic carbon is pre-coordinated to the metal center in the isonitrile precursor. Moreover, this procedure provided aeeess to a new subclass of abnormal carbenes and yielded the first abnormal earbene complexes featuring a saturated heteroeyele, unlike all previous abnormal imidazolylidene complexes, derived from unsaturated heteroeyeles. [Pg.128]


See other pages where Gold carbene direct is mentioned: [Pg.163]    [Pg.273]    [Pg.287]    [Pg.165]    [Pg.59]    [Pg.94]    [Pg.5]    [Pg.140]    [Pg.463]    [Pg.197]    [Pg.215]    [Pg.155]    [Pg.23]    [Pg.118]    [Pg.144]   
See also in sourсe #XX -- [ Pg.42 ]




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