Substitutions metal-free allylic

Scheme 26.10 Metal-free allylic substitution promoted by a chiral contact ion pair.

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). 

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 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... 

High selectivities with respect to (Z)-enolate formation (even without HMPA) can be obtained if R contains substituents with free electron pairs (O, N, S), which are able to coordinate to the enolate metal [Ik]. a-Substituted esters give rise to five-membered (A), and ) -substituted esters to six-membered chelate rings (B) (Figure 5.2.1). The same is true for the enolates obtained from secondary allyl amides (aza-Claisen rearrangement) [5j. 

Where X is Br or Cl, the free acids may be obtained by acidification of the alkaline solution, but where X is I, the acids must be isolated as salts to avoid reduction of the arsonic acids by HI. Rather than using alkyl halides, alkyl or dialkyl sulfates or alkyl arenesulfonates can be used. Primary alkyl halides react rapidly and smoothly, secondary halides react only slowly, whereas tertiary halides do not give arsonic acids. Allyl halides undergo the Meyer reaction, but vinyl halides do not. Substituted alkyl halides can be used eg, ethylene chlorohydrin gives 2-hydroxyethylarsonic acid [65423-87-2], C2H7As04. Arsinic acids, R sC OH), are also readily prepared by substituting an alkali metal arsonite, RAs(OM)2, for sodium arsenite ... 

AMMONIUM CHROMATE (7788-98-9) Not combustible but will enhance an existing fire. A powerful oxidizer. A heat- and shock-sensitive explosive. Contact with strong reducing agents such as hydrazine, alcohols, or ethers can cause explosion. Contact with water produces an alkaline solution, with evolution of free ammonia. Violent reaction with combustible materials, finely divided metals, organic substances. Aqueous solution is incompatible with organic anhydrides, acrylates, alcohols, aldehydes, alkylene oxides, substituted allyls, cellulose nitrate, cresols, caprolactam solution, epichlorohydrin, ethylene dichloride, isocyanates, ketones, glycols, nitrates, nitromethane, phenols, vinyl acetate. Exothermic decomposition with maleic anhydride. 

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