Allylic metal-free

Metallocorroles (M = Cu, Ni or Pd) can also be alkylated under the same conditions as the metal-free corroles23,24 to give the N2i-alkylated products together with a small amount of C3 alkylated product ( f = Pd). Allyl halides or bulky alkyl halides react with nickel corroles also at the 3-position. 

Assuming a reactive oxonium ylide 147 (or its metalated form) as the central intermediate in the above transformations, the symmetry-allowed [2,3] rearrangement would account for all or part of 148. The symmetry-forbidden [1,2] rearrangement product 150 could result from a dissociative process such as 147 - 149. Both as a radical pair and an ion pair, 149 would be stabilized by the respective substituents recombination would produce both [1,2] and additional [2,3] rearrangement product. Furthermore, the ROH-insertion product 146 could arise from 149. For the allyl halide reactions, the [1,2] pathway was envisaged as occurring via allyl metal complexes (Scheme 24) rather than an ion or radical pair such as 149. The remarkable dependence of the yield of [1,2] product 150 on the allyl acetal substituents seems, however, to justify a metal-free precursor with an allyl cation or allyl radical moiety. 

Another type of Cinchona alkaloid catalyzed reactions that employs azodicarbo-xylates includes enantioselective allylic amination. Jprgensen [51-53] investigated the enantioselective electrophilic addition to aUyhc C-H bonds activated by a chiral Brpnsted base. Using Cinchona alkaloids, the first enantioselective, metal-free aUyhc amination was reported using alkylidene cyanoacetates with dialkyl azodi-carboxylates (Scheme 12). The product was further functionalized and used in subsequent tandem reactions to generate useful chiral building blocks (52, 53). Subsequent work was applied to other types of allylic nitriles in the addition to a,P-unsaturated aldehydes and P-substituted nitro-olefins (Scheme 13). 

The two established pathways for transition metal-catalyzed alkene isomerization are the jr-allyl metal hydride and the metal hydride addition-elimination mechanisms. The metal hydride addition-elimination mechanism is the more common pathway for transition metal-catalyzed isomerization. In this mechanism, free alkene coordinates to a metal hydride species. Subsequent insertion into the metal-hydride bond yields a metal alkyl. Formation of a secondary metal alkyl followed by y3-elimination yields isomerized alkene and regenerates the metal hydride. The jr-allylhydride mechanism is the less commonly found pathway for alkene isomerization. Oxidative addition of an activated allylic C-H bond to the metal yields a jr-allyl metal hydride. Transfer of the coordinated hydride to the opposite end of the allyl group yields isomerized alkene. 

Allyl derivatives 11 with identical substituents at Cl and C3 are an important class of substrates for enantioselective allylic substitution (Scheme 10). Starting from either enantiomer (11 or ent-ll) the same allyl-palladium complex 12 is formed. Therefore, the first part of the catalytic cycle leading to this intermediate usually is irrelevant for the stereoselectivity of the overall reaction [31]. The two termini of the free allyl system are enantiotopic. If the catalyst is chiral, they become diasterotopic in the allyl-metal complex and, therefore, may exhibit different reactivities toward nucleophiles. Under the influence of a suitable chiral ligand attached to palladium, nucleophilic attack can be rendered regioselective leading preferentially either to product 13 or its enantiomer ent-l3. 

A third means of isomerization can be the anti attack of a free palladium(O) phosphane species onto the Ti-allyl-metal complex. Additionally, the 7r-allylpalladium complex can suffer epimer-ization through n-a-n rearrangement, especially, if one allyl terminus is unsubstituted. The degree of stereoselectivity is also a function of the reactivity of the nucleophile as well as of the substrate, the medium, the ligands employed and the catalyst used. Furthermore, the stereointegrity in the alkylation of some acylic substrates depends on the ionization from a single conformation. 

After precomplexation with ji-CD, a variety of alcohols, including aromatic alcohols, were oxidized to their corresponding carbonyl compounds in good yields with NaOCl-KBr in aqueous solution. A substrate-selective and transition metal-free oxidation of benzoic and allylic alcohols with NaOCl oxidant mediated by j8-CD in water was developed. In the presence of one molar equivalent of jS-CD, benzyl alcohol, 4-methoxybenzyl alcohol and some primary aromatic alcohols were oxidated to form benzaldehyde, 4-methoxybenzaldehyde and aromatic aldehydes, respectively, at 50 °C for 1-4 h. When 20% of acetone was added to the reaction system, the yield of aldehyde was dramatically decreased. 

Generated in situ amidoiodanes 458 and 459 are usehil reagents for metal-free direct allylic amination or diamination of alkenes [616,617]. 

A simple transition metal-free hydro/hydrothiophosphonylation of Baylis-Hillman adducts, such as substituted allyl bromides, allenylpho-sphonates and alkynes, promoted by fluoride ion in ionic liquids led to y-hydroxyphosphonates (301), a-phenyl allylphosphonate (302) and phosphonates (303-305), has been described by Swamy and co-workers. ... 

Swamy has reported a simple transition metal-free hydro/hydrothiophos-phonylation of MBH adducts, substituted allyl bromides, allenylphosphonates and alkynes, promoted by fluoride ion in an ionic liquid (Scheme 3.212). It was the first time that clear-cut evidence was provided for fluoride activation of the phosphite via pentacoordinate phosphorus. The reaction of cyclic phosphites 476 with various MBH adducts 477 in the presence of (n-Bu)4N F (TBAF) in [bmimj pFg] leads selectively to y-hydroxyphosphonates 479. In contrast, the corresponding reaction of 476a with MBH acetates affords P-CH2 allylphosphonates 481 with the elimination of acetic acid, " and the... 

Ammonium-directed metal-free oxidation of cyclic allylic and homoallylic amines has been reviewed. Such reactions yield all four diastereoisomers of the corresponding 3-amino-1,2-diols, and have featured in recent syntheses of ( )-l-deoxynojirimycin and ( )-l-deoxyaltronojirimycin. ... 

The formation of stabilized imino-iodanes as nitrene precursors has been exploited widely in aziridination of alkenes. Traditionally, isolated iminoiodanes have been the preferred route toward transition metal mediated or catalyzed aziridination or C-H amination chemistry [33]. Despite the great success in this field, some reports have become available on the corresponding transition metal-free variants. For example, Padwa reported an iodine(lll)-mediated aziridination of some carbamates 43 from allylic alcohols that in situ formed the corresponding imino-iodanes. Unexpectedly, these compounds underwent direct aziridination to the putative tricyclic compound 44, which was subsequently opened by addition of suitable nucleophiles to arrive at the 1,2-difunctionalized product 45 in a completely stereoselective manner (Scheme 11) [34]. This transformation constituted the proof of concept that iodine(lll)-mediated aziridination does not necessarily require metal promoters. 

Generation and Reactions of Metal-free Stannyl Anions from M SiSnBua and Highly Dissociated Fluorides. Aryl, vinyl, and allyl anions are easily generated by reactions of the appropriate precursor with Me3SiSnBu3 and a reactive fluoride source. Presumably, the reaction proceeds through a highly dissociated tributylstannyl anion. The examples (eqs 19-22) illustrate the use of various halide sources for the synthesis of these reactive intermediates. 

Abstract Selective functionalization of one specific C(sp )-H bond in a complex molecule without the assistance of a directing group represents the state of the art in organic synthesis and will be a dynamic topic in future. In the past decade, many excellent methods have been developed to accomplish this goal with transition-metal catalysts and even under metal-free conditions. In this chapter, we summarize the recent achievements in this realm during the past 5 years, including oxidative functionalization of a-C(sp )-H bonds adjacent to heteroatoms, allylic, benzylic, and unactivated aliphatic C(sp )-H bonds. The total redox-neutral C(sp )-H bond functionalization is also briefly introduced. 

In addition, beyond the transition-metal catalysts, much more recent works focused on the metal-free allylic C(sp )-H bond functionalization (Scheme 2.29) [144-147]. For example, Muniz et al. reported a metal-ffee, I(III)-mediated inter-molecular amination of allylic C-H bonds [144]. The hypervalent iodine(III) reagent acted as the oxidant, while bistosylimide was the real nitrogen source. 

Kabalka, G. W., Yao, M.-L., BoreUa, S., Wu, Z.-Z. 2005. Allylic aUcenylation of aUyhc alcohols using alkenylboron dihahdes A formal transition-metal free Suzuki reaction. Chem. Commun. 2492-2495. 

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