Highly efficient Cu(I)-catalyzed trifluoromethylation of aryl(heteroaryl) enol acetates with CF3 radicals derived from CF3SO 2Na and TBHP at room temperature
An efficient method for the Cu(I)-catalyzed synthesis of α-trifluoromethyl ketones via the addition of CF3 to aryl(heteroaryl) enol acetates by using the readily available CF 3SO2Na (Langlois reagent) has been developed. The reaction is experimentally simple and carried out at room temperature, providing good to excellent yields with wide functional group tolerance.
Hydration of Alkynes in Anhydrous Medium with Formic Acis as Water Donor
Formic acid has been found to hydrate alkynes in the absence of water to give oxo products and carbon monoxide.The scope of the reaction of alkynes and formic acid has been delineated.Hydrocarbon alkynes were found to be reactive in the absence of catalyst.Functionalized alkynes, in particular oxygenated alkynes, are inert toward formic acid but can be activated catalytically with Ru3(CO)12.Consequently, all the tested types of alkynes were found to give oxo products and CO with formic acid.The mechanism of the reaction was examined.With some alkynes, the primary oxo products underwent secondary reactions that gave rise to unexpected products.
Menashe, Naim,Shvo, Youval
p. 7434 - 7439
(2007/10/02)
Acetoxyselenenylation of Olefins for the Preparation of Vinylic and Allylic Acetates
Terminal and 1,2-disubstituted olefins were irreversibly acetoxyselenenylated by treatment with PhSeBr in an acetate buffer solution.Styrene derivatives yielded only Markovnikov adducts whereas simple terminal olefins and olefins containing an allylic oxygen substituent (acyloxy or aryloxy group) afforded significant amounts (50-85percent) of the anti-Markovnikov isomer.The product mixtures were isomerized to contain 90-97percent of the Markovnikov products by treatment with a catalytic amount (6-41percent) of BF3*OEt2 in chloroform.Oxidation (SO2Cl2/hydrolysis or MCPBA) of the isomerized products and selenoxide elimination at elevated temperature toward the acetoxy group afforded enol acetates in fair yields.The selenoxides of the anti-Markovnikov isomers (unisomerized mixtures) spontaneously eliminated, in the presence of the selenoxides of the Markovnikov isomer, to give allylic acetates in good yields at ambient temperature.
Engman, Lars
p. 884 - 890
(2007/10/02)
Two Regiocomplementary Approaches to Angular Furanocoumarins with Chromium Carbene Complexes: Synthesis of Sphondin, Thiosphondin, Heratomin, and Angelicin
Two regiocomplementary syntheses of the angular furanocoumarin sphondin are described utilizing the benzannulation reaction of furylcarbene complexes of chromium.The high regioselectivity of an intermolecular synthesis employing the reaction of pentacarbonylchromium (8) and methyl 4-pentynoate is thought to be controlled by the preferred conformation of an alkyne-carbene complex intermediate.By utilizing the same acetylene, heratomin and an unnatural derivative of sphondin, 6-methoxy-2-oxo(2H)-thiofuro(2,3-h)benzopyran were prepared from pentacarbonylchromium (37) and pentacarbonylchromium (31), respectively.An intramolecular synthesis of sphondin from oxy>carbene>pentacarbonylchromium (10e) incorporates the acetylene with reversed regiochemistry due to the geometrical constraints of the intramolecular annulation.Control over the formation of the regiochemistry correct for the carbon skeleton of sphondin is possible due to the regioselectivity in the annulation of unsymmetrical aromatic substituents (3-furyl) on the carbene carbon.The intramolecular synthesis is thus related to the intermolecular synthesis by a double reversal in the regiochemistry.A convergent synthesis of sphondin and angelicin is described which has the phenol 72 produced from the intramolecular benzannulation of complex 10e as a branch point and is differentiated by whether the phenol functionality is retained or reduced.
Wulff, William D.,McCallum, J. Stuart,Kunng, Fen-Ann
p. 7419 - 7434
(2007/10/02)
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