Terminal alkenes, oxidative arylation

Allyl aryl ethers undergo accelerated Claisen and [1,3] rearrangements in the presence of a mixture of trialkylalanes and water or aluminoxanes. The addition of stoichiometric quantities of water accelerates both the trimethylaluminum-mediated aromatic Claisen reaction and the chiral zirconocene-catalyzed asymmetric carboalumination of terminal alkenes. These two reactions occur in tandem and, after oxidative quenching of the intermediate trialkylalane, result in the selective formation of two new C-C bonds and one C-0 bond (Eq. 12.70).153 Antibodies have also been developed to catalyze Claisen154 and oxy-Cope155 rearrangements. 

Figure 16.4-1. Selected enzymatic oxidations of aldehydes. A oxidation of complex natural products such as retinal B oxidation of aliphatic and a,P-unsaturated aldehydes C oxidation of (hetero)arylic aldehydes D oxidative cleavage of the aldehyde-carbon atom yielding terminal alkenes.

The desulfitative Heck-type reaction of aryl sulfinic acids ArSOjH with terminal alkenes RCH=CH2, catalysed by (AcO)2Pd in the presence of (AcO)2Cu as oxidant, has been reported to produce the corresponding rra 5-alkenes RCH=CHAr no ligand or base is required. ... 

Scheme 8.74. The formation of a terminal alkene by an elimination reaction sequence that begins with the conversion of the oxygen of cyclohexylmethanol to a good leaving group through a reaction with tri- -butylphosphine and o-nitrophenyl selenocyanate to form the corresponding selenide (where the oxygen of the starting alcohol has been replaced with the aryl-substituted selenium). Subsequent oxidation to a selenoxide is followed by a rapid elimination to the desired alkene (methylenecyclohexane).

In the palladium-catalysed carbonylation of aryl bromides to yield benzaldehyde derivatives, IV-formylsaccharin is used as the source of the acyl function. A double carbonylation has been observed in the reaction of aryl halides with carbon monoxide and terminal alkenes which yields 4-arylfuranones such as (152). The proposed mechanism involves oxidative addition of the aryl halide to palladium and insertion of the carbon monoxide to give an acyl palladium species. This is followed by coordination and insertion of the alkene. A second carbon monoxide insertion is faster than -hydride elimination and, after intramolecular attack, leads to the product. The palladium-catalysed reaction of aryl iodides with simple ketones such as acetone in the presence of carbon monoxide has been shown to yield 1,3-diketones such as... 

Oxidative Heck reactions via Pd(II) C—H functionalization of terminal alkenes with pinacol boranes have been described for the preparation of styrenes and derivatives through electrophilic Pd(II) catalysis (Scheme 3.20). ° Treatment of a functionalized allylic precursor with the Pd(II) catalysts listed facilitated an allylic C—H activation. Subsequent transmetallation of the aryl boronic acid and reductive elimination afforded the desired olefin with excellent stereoselectivity. The scope of the transformation allows for a variety of activating and deactivating substituents on the aryl boronic acid as well as numerous functional groups on the starting alkene. A tandem allylic C—H oxidation/vinylic arylation protocol has also been reported. " ... 

SCHEME 3.20 Oxidative Heck arylation of terminal alkenes. 

Recently, Dong et al. reported a multicatalytic cascade reaction combining Pd, acid, and Ru catalysis [11]. By coupling palladium-catalyzed oxidation, acid-catalyzed hydrolysis, and ruthenium-catalyzed reduction, the elusive anti-Markovnikov olefin hydration was formally achieved, affording primary alcohols from waters and aryl-substituted terminal alkenes (Scheme 9.8). 

In contrast to SMOs, which exclusively catalyze the formation of (S)-epoxides, CPOs are able to yield chiral (P)-epoxides from styrene derivatives, which could serve as a stereocomplementary method (Scheme 13.11). However, the substrate spectrum appeared to be very limited [85,109]. Two ds-disubstituted aryl-substituted alkenes, czs-a-methylstyrene and 1,2-dihydronaphthalene, were effectively epoxi-dized in the presence of H Oj, and the later underwent spontaneous hydrolytic ring opening to afford the corresponding trans-diol. The enantiomeric excesses of the products were as high as 96% and 97% ee, respectively [83]. Terminal alkenes such as styrene and derivatives with a halide substituent on the benzene ring [109] or an alpha-alkyl substituent [85] could be accepted by CPO, and underwent epoxidation using f-BuOOH or HjOj as the oxidant, but the (P)-epoxides were achieved with only low to medium enantiopurity [83,85,109]. 

In Grignard reactions, Mg(0) metal reacts with organic halides of. sp carbons (alkyl halides) more easily than halides of sp carbons (aryl and alkenyl halides). On the other hand. Pd(0) complexes react more easily with halides of carbons. In other words, alkenyl and aryl halides undergo facile oxidative additions to Pd(0) to form complexes 1 which have a Pd—C tr-bond as an initial step. Then mainly two transformations of these intermediate complexes are possible insertion and transmetallation. Unsaturated compounds such as alkenes. conjugated dienes, alkynes, and CO insert into the Pd—C bond. The final step of the reactions is reductive elimination or elimination of /J-hydro-gen. At the same time, the Pd(0) catalytic species is regenerated to start a new catalytic cycle. The transmetallation takes place with organometallic compounds of Li, Mg, Zn, B, Al, Sn, Si, Hg, etc., and the reaction terminates by reductive elimination. 

Ni(II) complexes of cyclam and oxocyclam derivatives catalyze the epoxidation of cyclohexene and various aryl-substituted alkenes with PhIO and NaOCl as oxidants, respectively. In the epoxidation catalyzed by the Ni(II) cyclam complex using PhIO as a terminal oxidant, the high-valent nickel- complexes (e.g., LNiin-0, LNi=0, LNiin-0-... 

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