24195-40-2Relevant academic research and scientific papers
Reversal of enantioselectivity in aldol reaction: New data on proline/λ-alumina organic-inorganic hybrid catalysts
Sz?ll?si, Gyo?rgy,Fekete, Mónika,Gurka, András A.,Bartók, Mihály
, p. 478 - 486 (2014/06/24)
We report new results on the aldol reactions between aldehydes of three different types (aromatic, aliphatic and cycloaliphatic) and acetone/cycloalkanones as reaction partners, driven by organic-inorganic hybrid catalyst Pro/λ-Al2O3. In contrast to the homogeneous liquidphase reaction, over Pro/λ-Al2O 3reversal of the enantioselection in up to 20-40 % ee depending on the structure of the aldehyde was observed in reactions of acetone. Reversal of the ee in the presence of c-Al2O3cannot be generalized, as it has only been observed for acetone among the ketones studied by us. It was proven using methods of a great variety such as ultrasonic irradiation, reuse measurements on used catalyst and the filtrate of the first reaction, measurements on the L-Pro-L-Pro(OH) dipeptide, studies using mixtures of L-Pro and D-Pro that the organic-inorganic hybrid catalyst Pro/λ-Al 2O3formed in situ is responsible for reversal of the ee. In the reactions of cycloalkanones there is presumably competition between the liquid-phase and the surface reaction over Pro/ c-Al2O 3with preference for the former. Based on these results a surface reaction pathway was proposed. Although, the ees obtained under heterogeneous catalytic conditions are low, further studies may lead to application of this unusual phenomenon for obtaining chiral heterogeneous catalysts suitable for the preparation of the desired enantiomer of a chiral compound using the same chiral source. Springer Science+Business Media New York 2013.
Reactions of tin(IV) enolates obtained from O-stannyl ketyls under neutral free radical conditions
Enholm, Eric J.,Whitley, Paul E.,Xie, Yongping
, p. 5384 - 5390 (2007/10/03)
Under mild and neutral free radical conditions, an α,β-unsaturated ketone reacted with tributyltin hydride to produce an intermediate resonance-stabilized allylic O-stannyl ketyl. Upon subsequent hydrogen atom abstraction, a tin(IV) enolate was afforded which could be quenched with a variety of electrophiles and form new carbon-carbon bonds. Aldehydes react to produce aldol-type products and both intramolecular and intermolecular carbonyl addition reactions were investigated using this strategy. Using similar methodology, the tin(IV) enolate could be quenched in the presence of HMPA with various alkyl halides and α,β-unsaturated carbonyl compounds (Michael acceptors) to yield alkylated products in good yields. These reactions represent a very mild regioselective alternative to metal enolate formation which usually requires strong bases such as LDA or strongly reductive dissolving metal conditions to achieve success. New carbon skeletons for natural product synthesis can be readily constructed using this chemically neutral approach.
INTERMOLECULAR ALDOL REACTIONS VIA ALLYLIC O-STANNYL KETYLS
Enholm, Eric J.,Whitley, Paul E.
, p. 9157 - 9160 (2007/10/02)
A mild and neutral free radical reaction of an α,β-unsaturated ketone and tributyltin radical produced a resonance-stabilized allylic O-stannyl ketyl intermediate.A tin(IV)enolate, produced by subsequent hydrogen atom transver, was next quenched with various aldehydes to yield an aldol product which was readily eliminated with p-toluenesulfonic acid to afford new α,β-unsaturated ketones with E/Z ratios up to > 100:1.
FACILE ALKYLATION OF o-HYDROXYARYLALDEHYDES AND α-FORMYLKETONES WITH TRIALKYLBORANES
Okada, Keiji,Hosoda, Yasushi,Oda, Masaji
, p. 6213 - 6216 (2007/10/02)
Trialkylboranes readily undergo alkylation reactions with o-hydroxyarylaldehydes and α-formylketones via the dialkylboryl complexes.
