Recent developments in the metal-catalyzed reactions of metallocarbenoids from propargylic esters.
The transition-metal-catalyzed intramolecular cycloisomerization of propargylic carboxylates provides functionalized bicyclo[n.1.0]enol esters in a very diastereoselective manner and, depending on the structure, with partial or complete transfer of chirality from enantiomerically pure precursors. The subsequent methanolysis gives bicyclo[n.1.0] ketones, hence resulting in a very efficient two-step protocol for the syntheses of alpha,beta-unsaturated cyclopropyl ketones, key intermediates for the preparation of natural products. The results from mechanistic computational studies suggest that they probably proceed through cyclopropyl metallocarbenoids, formed by endo-cyclopropanation, that undergo a 1,2-acyl migration. Finally, the potential of the intermolecular reaction and the related pentannulation of propargylic esters bearing pendant aromatic rings are also discussed.
Marco-Contelles
José
J
Laboratorio de Radicales Libres, Instituto de Química Orgánica General (CSIC) c/Juan de la Cierva, 3, 28006 Madrid, Spain.
Soriano
Elena
E
D000480:Alkynes / Q000737:chemistry*; D001688:Biological Products / Q000138:chemical synthesis*; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000138:chemical synthesis*; D002384:Catalysis; D003500:Cyclization; D003521:Cyclopropanes / Q000737:chemistry; D004952:Esters / Q000138:chemical synthesis*; D006838:Hydrocarbons / Q000737:chemistry; D007659:Ketones / Q000138:chemical synthesis; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D000432:Methanol / Q000737:chemistry; D008956:Models, Chemical; D009942:Organometallic Compounds / Q000737:chemistry*; D020005:Propanols / Q000737:chemistry*; D013237:Stereoisomerism; D028561:Transition Elements / Q000737:chemistry*
D000480:Alkynes; D001688:Biological Products; D019086:Bridged Bicyclo Compounds, Heterocyclic; D003521:Cyclopropanes; D004952:Esters; D006838:Hydrocarbons; D007659:Ketones; D009942:Organometallic Compounds; D020005:Propanols; D028561:Transition Elements; C030011:carbene; C028255:propargyl alcohol; D008697:Methane; D000432:Methanol