Preparation of sigma- and pi-allylicopper(III) intermediates in S(N)2 and S(N)2 ' reactions of organocuprate(I) reagents with allylic substrates

The first pi-allyl complexes of Cu(III) have been prepared and characterized by using rapid injection nuclear magnetic resonance spectroscopy (RI-NMR). The prototype, (eta(3)-allyl) dimethylcopper(III), was prepared by injection of allyl chloride into a THF-d(8) solution of iodo-Gilman reagent, Me(2...

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Published inJournal of the American Chemical Society Vol. 130; no. 34; pp. 11244 - 11246
Main Authors Bartholomew, Erika R., Bertz, Steven H., Cope, Stephen, Murphy, Michael, Ogle, Craig A.
Format Journal Article
LanguageEnglish
Published WASHINGTON Amer Chemical Soc 27.08.2008
Subjects
Chemistry
Chemistry, Multidisciplinary
Physical Sciences
Science & Technology
GILMAN
COPPER(III) INTERMEDIATE
SUBSTITUTION
ORGANOCOPPER CHEMISTRY
MECHANISM
LIGANDS
PI-COMPLEXES
RAPID-INJECTION NMR
CONJUGATE ADDITION
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Summary:The first pi-allyl complexes of Cu(III) have been prepared and characterized by using rapid injection nuclear magnetic resonance spectroscopy (RI-NMR). The prototype, (eta(3)-allyl) dimethylcopper(III), was prepared by injection of allyl chloride into a THF-d(8) solution of iodo-Gilman reagent, Me(2)CuLi .Lil (A), spinning in the probe of an NMR spectrometer at -100 degrees C. A sigma-allyl ate complex, lithium (eta(1)-allyl)trimethylcuprate(III), was prepared in high yield by including 1 equiv of tributylphosphine in the reaction mixture or by using allyl acetate as the substrate, Cyano ate complex, lithium cis-(eta(1)-allyl)cyanodimethylcuprate(III) was obtained in high yield by injecting allyl chloride or allyl acetate into the cyano-Gilman reagent, Me(2)CuLi .LiCN (B), in THF-d(8) at -100 degrees C. Reactions of A with allylic substrates show a definite dependence on leaving group (chloride vs acetate), whereas those of B do not. Moreover. these reagents have different regioselectivities, which in the case of A vary with temperature. Finally, the exclusive formation of cis-cyano sigma-allyl Cu(III) intermediates in both the 1,4-addition of B to a-enones and its S(N)2a reaction with allylic substrates now makes sense in terms of pi-allyl intermediates in both cases, thus unifying the mechanisms of these two kinds of conjugate addition.
ISSN:0002-7863
DOI:10.1021/ja801186c