Transfer intermolecular allyl

Enamines derived from ketones are allylated[79]. The intramolecular asymmetric allylation (chirality transfer) of cyclohexanone via its 5-proline ally ester enamine 120 proceeds to give o-allylcyclohexanone (121) with 98% ee[80,8l]. Low ee was observed in intermolecular allylation. Similarly, the asymmetric allylation of imines and hydrazones of aldehydes and ketones has been carried out[82]. 

In Equation 16, the first step is the activation of a cyclohexene molecule by electron impact, and the second step is the reaction of the activated cyclohexene molecule with a normal cyclohexene molecule resulting in intermolecular allylic hydrogen transfer. In Equation 17 the first step is ionization of a cyclohexene molecule by electron impact, and... 

Miscellaneous Reactions. Allji alcohol can be isomerized to propionaldehyde [123-38-6] in the presence of solid acid catalyst at 200—300 0. When copper or alumina is used as the catalyst, only propionaldehyde is obtained, because of intramolecular hydrogen transfer. On the other hand, acrolein and hydrogen are produced by a zinc oxide catalyst. In this case, it is considered that propionaldehyde is obtained mainly by intermolecular hydrogen transfer between allyl alcohol and acrolein (31). 

Intermolecular allyl, propargyl, and allenyl ligand transfer... 

The ophcally active Pd complex with a chiral allenyl ligand undergoes epimer-izahon in the presence of a catalytic amount of Pd(0) complex. This reaction does not involve the isomerization to the propargyl complex, but takes place via a dinuclear intermediate as depicted in Scheme 5.39. The -allenyl ligand in the dinuclear palladium intermediate may racemize via a vinyl-vinyidene intermediate. This type of reaction is prohahly involved in a kinetic resolution of racemic propargyl alcohols promoted hy chiral transihon metal complex [203]. The intermolecular allyl ligand transfer from Pd to Ee complexes occurs under... 

It was believed for a long time that head-to-head radical addition to monomers is a major route for formation of labile structures. Kinetic studies, in association with NMR measurements, reveal that formation of internal allylic and tertiary chlorine structures actually proceeds through an intramolecular or intermolecular chain-transfer reaction to polymer [Eqs. (31), (32) VC = vinyl chloride]. 

As shown in the manganese- and ruthenium-catalyzed intermolecular nitrene insertions, most of these results supposed the transfer of a nitrene group from iminoiodanes of formula PhI=NR to substrates that contain a somewhat activated carbon-hydrogen bond (Scheme 14). Allylic or benzylic C-H bonds, C-H bonds a to oxygen, and very recently, Q spz)-Y bonds of heterocycles have been the preferred reaction sites for the above catalytic systems, whereas very few examples of the tosylamidation of unactivated C-H bonds have been reported to date. 

Mechanisms III and IV both predict that Ha in 10 (Scheme 12.8) migrates to the terminal carbon on the opposite allylic chain and becomes part of a methyl group. However, in mechanism III Ha migrates intramolecularly whereas in IV the migration is intermolecular via 14. The deployment of a mixed 13C/D-labelled substrate (experiment (iii), Scheme 12.9) allows this distinction to be made as products are obtained in which D has transferred intermolecularly (see the right-hand product in experiment (iii), which demonstrates crossover of D). 

Methylation and benzylation of the pyrrolidine dienamine of 3-methyl-A "-2-octa-lone gives a mixture of N- and jS-alkylated products in protic and aprotic solvents. However, the position of attack by acrylonitrile and methyl acrylate is solvent-dependent. In protic solvents the / -alkylated octalone is obtained on hydrolysis, whereas in aprotic solvents the -alkylated product is produced (Scheme 7). This change in the regioselectivity arises from the C-3 methyl group being forced into a quasi-axial orientation because of allylic strain in the equatorial orientation. As a consequence the carbanionic centre in the initially formed zwitterion 6 cannot be neutralized by an internal proton transfer of an axial proton at C-3. In protic solvents intermolecular protonation renders the reaction irreversible, but in aprotic solvent reversion to starting material occurs. This allows 5- or -alkylation to occur and this is rendered irreversible by internal proton transfer from the 6 - or 5-position, respectively, to the carbanionic centre in the resulting zwitterion (Scheme 7). 

Racemization by this mechanism seems to be a general problem for allyl esters and phosphates since, as the following discussion shows, successful chirality transfer in intermolecular reactions is observed only for 1,3-disubstituted 7i-allyl complexes, which cannot racemize via this pathway. 

The most important synthetic asset of the xanthate transfer methodology lies in its ability to induce carbon-carbon bond formation by intermolecular addition to unactivated olefins. Again, this is possible because the initial radical has a comparatively long lifetime in the medium. Unhindered, terminal olefins are the best substrates, but other types of olefins (especially strained or lacking allylic hydrogens) may be made to react in some cases. Three examples of additions are collected in Scheme 18. The first involves formation and capture of a trifluoroacetonyl radical, a species hitherto only studied by mass spectrometry but never employed in synthesis [34a]. This reaction represents a convenient route to various, otherwise inaccessible, trifluoromethyl ketones. In the second example a tetrazolylmethyl radical, also a previously unused intermediate, is intercepted by a latent allyl glycine [34b]. The amino acid moiety may be part of the xanthate partner as highlighted by the last example [34c]. 

Transmetalation of jt-allyl transition metal complexes and of the complexes with related C3 ligands proceeds via unique pathways that are not found in the intermolecular transfer of -bonded organic ligands. Rich information about stereochemistry of unsymmetrically substituted rt-allyl ligands of Pd complexes provides a useful probe to investigate details of the reaction mechanism. Cationic jr-allylpalladium(II) complex reacts with ethylene-coordinated Pt(0) complex to afford the jr-allylplatinum(II) complex and Pd(0) complex via transfer of the allyl ligand from Pd to Pt (Eq. 5.57). 

Besides allyl, benzyl, and methyl groups also migrate/In every case, the reaction is intermolecular with an induction period involving equilibration of the allylic termini (in that case) and is inhibited by thiophenol, and related chain-transfer agents clearly indicating free radical processes. 

However, recently, isolated and fully characterized iron porphyrin carbene complexes such as (TPFPP)Fe(CPh2)(MeIm) [61], have been found to react with hydrocarbons to form C - H insertion products. For example, they can undergo carbon atom transfer into benzylic C - H bonds of cumene or into allylic C - H bonds of cyclohexene. These complexes can also cyclopropanate alkenes without photolysis and undergo intermolecular carbon atom transfer into saturated C - H bonds. 

For the preparation of C-glycosides, a hydrogen-atom transfer (HAT)/ intermolecular radical allylation process has been devised as a new methodology (Scheme 5.45) [69]. Through the reaction of207 with aUyltri-n-butyltin, a radical 208... 

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