Propargyl Chlorides as Sources for Cobalt Stabilized .gamma.-Carbonyl Cations
作者:C. Stephen Vizniowski、James R. Green、Tricia L. Breen、Andrea V. Dalacu
DOI:10.1021/jo00128a022
日期:1995.11
Hexacarbonyldicobalt complexes of gamma-chloroalkynones and gamma-chloroalkynoates (5) were found to undergo silver-mediated Nicholas condensation reactions with silyl enol ethers or silyl ketene acetals (10) to give 1,6-dicarbonyl complexes 11 in fair to good yields. Substrates 5 with gamma-alkyl substitution formed diastereomeric products with enol silanes 10a and 10b. Reactions with propiophenone trimethylsilyl enol ether (10b) gave good levels of syn diastereoselection, whereas reactions with cyclohexanone trimethylsilyl enol ether (10a) were only slightly diastereoselective, favoring the anti diastereomer. When conducted in acetonitrile, the silver-mediated reaction of 5e gave a radical dimerization product 13, isolated as the syn diastereomer.
Bifunctional phosphine ligand-enabled gold-catalyzed direct cycloisomerization of alkynyl ketones to 2,5-disubstituted furans
An efficient synthesis of 2,5-disubstitutedfurans directly from alkynyl ketones has been developed via tandem gold(I)-catalyzed isomerization of alkynyl ketones to allenyl ketones and cycloisomerization. The key to the success of this chemistry is the use of a biphenyl-2-ylphosphine ligand featuring a critical remote tertiary amino group.