28790-87-6Relevant academic research and scientific papers
Asymmetric enamine catalysis with β-ketoesters by chiral primary amine: Divergent stereocontrol modes
Xu, Changming,Zhang, Long,Luo, Sanzhong
, p. 11517 - 11526 (2015/01/09)
α-Branched ketones remain a challenging type of substrates in aminocatalysis due to their congested structures as well as the associated difficulties in controlling chemo- and stereoselectivity. In this work, we have explored asymmetric aminocatalysis with α-substituted β-ketoesters. A simple chiral primary amine catalyst was identified to enable unprecedentedly effective catalysis of β-ketoesters in α-hydrazination and Robinson annulation reaction with good yields and high enantioselectivities. Stoichiometric experiments with preformed enamine ester intermediates revealed their enamine-catalytic nature as well as the critical roles of acidic additives in facilitating catalytic turnovers and in tuning the chemo- and stereoselectivity. With the identical catalytic system, the two reactions demonstrated opposite chiral inductions in terms of the absolute configurations of the newly formed stereogenic centers. Investigations into this intriguing issue by DFT have revealed divergent stereocontrol modes. For α-hydrazination, H-bonding-directed facial attack determines the stereoselectivity, whereas a steric model is applied to the Robinson annulation where dual activations of both β-ketoester and vinyl ketone/aldehyde are involved.
The Conversion of Ethyl Dienol Ether and Dienyl Pivalate Derivatives of Hagemann's Ester into Bicyclic Enones
Baker, Murray V.,Ghitgas, Christine,Dancer, Robert J.,Haynes, Richard K.,Sherwood, Gloria V.
, p. 1331 - 1340 (2007/10/02)
The cyclization of compounds obtained from ethyl dienol ether and dienyl pivalate derivatives of Hagemann's ester has been examined.The carbanions of methyl phenyl sulfone and methyl phenyl sulfoxide react with the methylated dienol ether (4) to give the
The Preparation of Ethyl and Isopropyl Dienol Ethers and Dienol Pivalate Esters from Hagemann's Ester and its t-Butyl Analouge, and the Reactions of the Derived Ester Dienolates with Electrophiles
Baker, Murray V.,Ghitgas, Christine,Haynes, Richard K.,Hilliker, Audrey E.,Lynch, Gregory J.,et al.
, p. 2037 - 2058 (2007/10/02)
The preparation of ethyl 4-ethoxy-2-methylcyclohexa-1,3-diene-1-carboxylate, ethyl 4-isopropoxy-2-methylcyclohexa-1,3-diene-1-carboxylate, t-butyl 4-isopropoxy-2-methylcyclohexa-1,3-diene-1-carboxylate, ethyl 4-(t-butylcarbonyloxy)-2-methylcyclohexa-1,3-diene-1-carboxylate, and t-butyl 4-(t-butylcarbonyloxy)-2-methylcyclohexa-1,3-diene-1-carboxylate from Hagemann's ester and its t-butyl analogue in the presence of diethyl or diisopropyl sulfates and sodium hydride in dimethyl sulfoxide, or pivaloyl chloride and N,N,N',N'-tetramethylethylenediamine in tetrahydrofuran is described.The foregoing dienol ethers and esters are smoothly deprotonated by lithium diisopropylamide in tetrahydrofuran at -78 deg C to give corresponding ester dienolates, which react regiospecifically with a number of electrophiles, either α or γ to the alkoxycarbonyl group of the dienol ether or ester.A number of the products, which are generally obtained in good yields, have been hydrolysed to Hagemann's ester dirvatives substituted exclusively at C 1.
ZUR REGIOSELEKTIVITAET BEIM ALDOL-RINGSCHLUSS
Kreiser, Wolfgang,Below, Peter
, p. 429 - 432 (2007/10/02)
According to the proper choice of reaction conditions, a regioselective ring closure of the 1,5-diketones I is achieved, either to II or III.This directed aldolisation was successfully applied to a short synthesis of the monoterpenoid piperitone.
