Oxidant-free alkenylation reaction

The substitution of aluminum by oxygen can be effected by various peroxide derivatives, such as di-r-butyl peroxide, benzoyl peroxide and r-butyl perbenzoate. The main reaction is accompanied by telltale free-radical side reactions, such as the formation of RR from R3AI, which become major pathways with aryl and vinyl compounds. Oxidation of alkenyl derivative (56) with r-butyl perbenzoate yields 45% of a mixture of cis and trans ethers (57 equation 44). As of yet there is no generally applicable, highly efficient method for oxidizing vinylaluminum compounds. 

Aryl and alkyl-substituted diynes and tetraynes have been synthesized in good yields (82-99%) by TBAF-promoted desily-lation and Cu-catalyzed oxidative dimerization of triisopropylsi-lyl (TlPS)-protected acetylenes (eq 38). Copper acetate was used as oxidant in this reaction. Aryl- and alkenyl alkynes were made under similar conditions (eq 39). Pd/C with TBAF was used in ligand- and copper-free, one-pot, domino Halex-Sono-gashira reactions. Similarly, TBAF promoted the synthesis of 2-substituted indoles by a tandem Sonogashira/cyclization reaction of 2-iodoanilines and terminal alkynes. ... 

The entropically enhanced cycloaddition rate of an intramolecular cycloaddition permits alkenyl nitrile oxides to cyclize in the presence of free amino groups, in contrast to intermolecular reactions. Since nitrile oxides have a wide spectrum of possible intermolecular reactions, they also react well in macro-cyclic cyclizations. 

In all of the aforementioned cases, the palladium(II)-catalysed indole alkenylation occurred preferentially at the 3-position of the indole moiety, which is consistent with the natural reactivity of indole towards electrophihc aromatic substitution reactions. More recently, a palladium(ll)-catalysed direct oxidative coupling of indole and alkenes was described by Gaunt and coworkers [28] that exploits a selective, solvent-controlled C—H functionalization of free NH indoles and leads to the substitution of the indole core at either the 2- or the 3-position. 

In situ generated, Ni(0)-alkyne complexes are also involved in Ni-catalyzed head-to-head dimerization of terminal alkynes (Equation (4)). In these reactions, the in situ generated Ni-(terminal alkyne) intermediates are thought to react by oxidative addition of the G -H bond to produce Ni qhydrido)(cr-alkynyl) species the latter then insert a free alkyne into the Ni-H moiety to produce an (alkenyl)(alkynyl) intermediate, which reductively eliminates to give enynes and regenerate the Ni(0) catalyst. 

Under ruthenium catalysis, oxidative coupling of a,a-disubstituted benzy-lamines with acrylates can be performed efficiently at room temperature to produce (isoindol-l-yl)acetic acid derivatives (Eq. (7.48)) [58]. The reaction takes place accompanied by free amino group-directed orffio-alkenylation and successive intramolecular cyclization. 

It seems that palladium complexes with high oxidative states and basic ligands can be involved in oxidative addition as weU as in o-bond metathesis. Cheng has demonstrated that phosphine-free Pd complexes together with alkenyl or aryl iodides are very efficient catalysts for 1,2-diboration of allenes. This reaction is completely regioselective and highly... 

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