Simple Metal Alkoxides as Effective Catalysts for the Hetero-Aldol−Tishchenko Reaction
摘要:
[GRAPHICS]This paper reports the utility of simple metal alkoxides for the catalytic, stereoselective hetero-aldol-Tishchenko reaction (eq 1), Choice of metal alkoxide is crucial to achieving high efficiency and stereoselectivity, Whereas NaO-t-Bu is an effective catalyst, delivering one product in 68% yield and 99:1 stereoselection, Sm(O-i-Pr)(3) is less effective and delivers the same product in 42% yield with 4:1 stereoselection.
作者:Teruaki Mukaiyama、Nobuharu Iwasawa、Rodney W. Stevens、Toru Haga
DOI:10.1016/s0040-4020(01)82423-6
日期:1984.1
A highly diastereoselective cross aldolreaction is developed using divalent tin enolates formed from stannous trifluoromethanesulfonate and carbonyl compounds. The reaction is extended to a highly enantioselective cross aldolreaction employing chiral diamines derivedfrom (S)-proline as ligands.
STANNOUS TRIFLATE: A NEW ALDOL REACTION VIA DIVALENT TIN ENOLATES
作者:Teruaki Mukaiyama、Rodney. W. Stevens、Nobuharu Iwasawa
DOI:10.1246/cl.1982.353
日期:1982.3.5
Divalent tin enolates formed from stannous triflate and ketones react with carbonyl compounds under mild conditions to give the corresponding aldol products in good yields. In the case of cross-cou...
The cross-aldol reaction between a ketone and an aldehyde proceeded smoothly with threo diastereoselection favorably mediated by ytterbium trifluoromethanesulfonate and tertiary amine in diethyl ether or in dichloromethane. A ytterbium enolate was trapped with chlorotrimethylsilane to afford a silyl enol ether.
Lithium Hexamethyldisilazide-Mediated Enolizations: Influence of Triethylamine on <i>E</i>/<i>Z</i> Selectivities and Enolate Reactivities
作者:Peter F. Godenschwager、David B. Collum
DOI:10.1021/ja800250q
日期:2008.7.1
Lithium hexamethyldisilazide (LiHMDS) in triethylamine (Et 3N)/toluene is shown to enolize acyclic ketones and esters rapidly and with high E/ Z selectivity. Mechanistic studies reveal a dimer-based mechanism consistent with previous studies of LiHMDS/Et 3N. E/ Z equilibration occurs when <2.0 equiv of LiHMDS are used. Studies of the aldolcondensation and Ireland-Claisen rearrangement of the resulting
titanium enolates of α-seleno esters in the presence of Ph3P or Ph3PO gave the products with high stereoselectivity favoring the syn isomers. Reaction of α-seleno ketones with TiCl4 in the presence of 2 equiv. of Et3N, and subsequently with aldehydes, gave the aldol products with high syn selectivity. The stereoselectivity in the aldol reaction of 3-pentanone also increased by using an excess amount of Et3N