Catalytic asymmetricPauson–Khandreactions with chiral bidentate phosphines as ligands have been successfully accomplished. The catalytic use of (S)-BINAP as a ligand was demonstrated to be the most effective in the cobalt-catalyzed reactions of 1,6-enynes, providing a facile entry to optically active 2-cyclopentenone derivatives with high enantioselectivity. A plausible mechanism for the asymmetric induction
Catalytic Asymmetric Cyclocarbonylation of Nitrogen-Containing Enynes
作者:Shana J. Sturla、Stephen L. Buchwald
DOI:10.1021/jo990384f
日期:1999.7.1
The asymmetric Pauson-Khand type cyclization of nitrogen-containing enynes using carbon monoxide and a catalytic amount of (EBTHI)TiMe(2) was examined. The influence of the nitrogen substituent and the concentration of the catalyst on the enantioselectivity of this cyclization was explored, and it has been found that enynes with an octyl-, benzyl-, or allylamino group, positioned beta to the alkyne
Allyl cyanides are found to add across alkynes in the presence of a nickel/P(4-CF3-C6H4)(3) catalyst to give polysubstituted 2,5-hexadienenitriles with defined stereo- and regiochemistry. Use of AlMe2Cl or AlMe3 as a Lewis acid cocatalyst accelerates the reaction and expands the substrate scope significantly. The cyano group in the allylcyanation products can be transformed to a hydroxymethyl or aminomethyl group to afford highly substituted allylic alcohols or amines. alpha-Siloxyallyl cyanides also add across alkynes selectively at the less hindered gamma-carbon to allow introduction of 3-oxo-propyl functionality after hydrolysis of the resulting silyl enol ethers. This particular carbocyanation reaction has been applied to the stereoselective construction of the trisubstituted double bond of plaunotol, an antibacterial natural product active against Helicobacter pylori.
Cyclization of 1,6-Enynes with Allylic Chromate Species
[GRAPHICS]Treatment of 1,6-enynes with tetramethallylchromate induces a cyclization reaction with concurrent introduction of a methallyl group. A catalytic amount of CrCl3 combined with methallyl magnesium chloride also achieves this cyclization process. The resultant cyclic organometallic species undergo further functionalization upon reaction with electrophiles.
Iron-Catalyzed, Hydrogen-Mediated Reductive Cyclization of 1,6-Enynes and Diynes: Evidence for Bis(imino)pyridine Ligand Participation
作者:Kevin T. Sylvester、Paul J. Chirik
DOI:10.1021/ja902478p
日期:2009.7.1
The bis(imino)pyridine iron dinitrogen complex (((i)Pr)PDI)Fe(N(2))(2) catalyzes the hydrogen-mediated reductivecyclization of enynes and diynes with turnover frequencies comparable to those of established precious metal catalysts. Amino, oxygenated, and carbon-based substrates are readily cyclized to the corresponding hetero- and carbocycles with 5 mol % iron and 4 atm H(2) at 23 degrees C. Stoichiometric