Allylic exchange

The Allylic Exchange of RCHaCH with HCo(CO)4 A second scheme for the isomerization of olefins by HCo(CO)4 consists of an exchange of an allylic hydrogen of the olefin with the hydrogen of the hydrocarbonyl through a six-membered transition state 18) ... 

In contrast to the other nickel complexes discussed here, that formed by (TjM.HCHj QHsljNi with P(CH3)3 has the 16-electron structure 26 in which fast r)1 rj3-allyl exchange occurs even at -95°C. As a result of... 

One potentially very useful synthetic reaction in Pd(II) catalysis is the vinyl and allylic exchange reactions,... 

Also the allylic exchange work indicated that nucleophiles do not like to attack the negatively charged monomeric it complex (Section III, B, 1). Furthermore, the kinetics of hydration of vinyl esters in wet acetic... 

If isomerization does not result from the addition of one hydrogen atom and the removal of another, it could result from the removal of a hydrogen atom and subsequent addition of hydrogen at another position. We suggest, then, that double-bond migration, process (7), results from heterolytic dissociative adsorption of olefin to a proton and adsorbed allyl. Exchange without isomerization, process (5), will not originate in dissociative adsorption to form -011=011—R since such a process should lead to ethylene-d, which is not observed. Both processes (5) and (7) could result from an allylic intermediate of one of two types. 

HMPA, through which a carbonylative coupling of aUyl and alkyl groups proceeds to provide unsymmetrical ketone and Pd(0) species. On the other hand, in the absence of HMPA, an alkyl-allyl exchange reaction takes place between I and organozinc and gives rise to the mixture of symmetrically substituted dialkylpalladium HI and allylzinc. Car-bonylation of the intermediate HI produces symmetrical ketone and regenerates Pd(0). Allylzinc thus formed is responsible for the formation of the lactones and the homoallyl alcohol in Scheme 26. ... 

M(allyl)4], however, shows fluxional behavior above 70°C (M = Mo) or above 90 C (M = W) with both syn-anti exchange and syn-syn (anti-anti) exchange which can be identified separately by magnetization transfer as the nonequivalent ends of the rj -allyl exchange. tj -Allyl species are involved as intermediates. 

Me2SiCH=CRCR (X)CH2 (X=0C(O)NHPh,0C(S)SMe R,R =H,Me) gives siloles, R,R =Me being the first methyl one stable as a monomer, as is the germole. Both undergo allyl exchange at the hetero-atom with RLi,... 

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