- Traceless chelation-controlled rhodium-catalyzed intermolecular alkene and alkyne hydroacylation
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A new functional-group tolerant, rhodium-catalyzed, sulfide-reduction process is combined with rhodium-catalyzed chelation-controlled hydroacylation reactions to give a traceless hydroacylation protocol. Aryl- and alkenyl aldehydes can be combined with both alkenes, alkynes and allenes to give traceless products in high yields. A preliminary mechanistic proposal is also presented. Traceless catalysis: The powerful combination of a chelation-controlled hydroacylation process and a new rhodium-catalyzed sulfide reduction gave the products of traceless hydroacylation. Aryl- and alkenyl aldehydes can be combined with alkenes, alkynes, and allenes to deliver traceless products in high yields (see scheme). Copyright
- Hooper, Joel F.,Young, Rowan D.,Weller, Andrew S.,Willis, Michael C.
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- Intermolecular hydroacylation: High activity rhodium catalysts containing small-bite-angle diphosphine ligands
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Readily prepared and bench-stable rhodium complexes containing methylene bridged diphosphine ligands, viz. [Rh(C6H5F)(R 2PCH2PR'2)][BArF4] (R, R' = tBu or Cy; ArF = C6H3-3,5- (CF3)2), are shown to be practical and very efficient precatalysts for the intermolecular hydroacylation of a wide variety of unactivated alkenes and alkynes with β-S-substituted aldehydes. Intermediate acyl hydride complexes [Rh(tBu2PCH 2PtBu2)H{κ2(S,C)-SMe(C 6H4CO)}(L)]+ (L = acetone, MeCN, [NCCH 2BF3]-) and the decarbonylation product [Rh(tBu2PCH2PtBu2)(CO) (SMePh)]+ have been characterized in solution and by X-ray crystallography from stoichiometric reactions employing 2-(methylthio) benzaldehdye. Analogous complexes with the phosphine 2-(diphenylphosphino) benzaldehyde are also reported. Studies indicate that through judicious choice of solvent and catalyst/substrate concentration, both decarbonylation and productive hydroacylation can be tuned to such an extent that very low catalyst loadings (0.1 mol %) and turnover frequencies of greater than 300 h-1 can be achieved. The mechanism of catalysis has been further probed by KIE and deuterium labeling experiments. Combined with the stoichiometric studies, a mechanism is proposed in which both oxidative addition of the aldehyde to give an acyl hydride and insertion of the hydride into the alkene are reversible, with the latter occurring to give both linear and branched alkyl intermediates, although reductive elimination for the linear isomer is suggested to have a considerably lower barrier.
- Chaplin, Adrian B.,Hooper, Joel F.,Weller, Andrew S.,Willis, Michael C.
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supporting information; experimental part
p. 4885 - 4897
(2012/05/04)
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