59554-08-4Relevant academic research and scientific papers
Catalytic asymmetric phase-transfer reactions using tartrate-derived asymmetric two-center organocatalysts
Ohshima, Takashi,Shibuguchi, Tomoyuki,Fukuta, Yuhei,Shibasaki, Masakatsu
, p. 7743 - 7754 (2007/10/03)
A new highly versatile asymmetric two-center catalyst, tartrate-derived diammonium salt (TaDiAS), was designed and a catalyst library containing more than 70 new two-center catalysts was constructed. A variety of (S,S)- and (R,R)-TaDiAS were easily synthesized from diethyl L- and D-tartrate, respectively, using common and inexpensive reagents under operationally simple reaction conditions. TaDiAS was used in phase-transfer alkylations and Michael additions to afford various optically active α-amino acid equivalents in up to 93% yield. Moreover, dramatic counter anion effects were observed in phase-transfer catalysis (PTC) for the first time, making it possible to further improve reactivity and selectivity. These findings validate the usefulness of three-dimensional fine-tuning of the catalyst (acetal, Ar, and counter anion) for optimization. Recovery and reuse of the catalyst was also possible using simple procedures. The present asymmetric PTC was successfully applied to enantioselective syntheses of serine protease inhibitor aeruginosin 298-A and its analogues.
Trifluoroacetylation of unsymmetrical ketone acetals. A convenient route to obtain alkyl side chain trifluoromethylated heterocycles
Bonacorso, Helio G.,Martins, Marcos A.P.,Bittencourt, Sandra R.T.,Lourega, Rogerio V.,Zanatta, Nilo,Flores, Alex F.C.
, p. 177 - 182 (2007/10/03)
A convenient method to obtain β-alkyl-β-methoxyvinyl trifluoromethyl ketones [CF3COCHC(OMe)R, where R = Et, n-Pr, i-Pr, i-Bu, t-Bu, -(CH2)2OMe] from the regiospecific acylation of kinetic enol ether generated in situ is reported. The unsymmetrical ketone dimethyl acetals react with trifluoroacetic anhydride in the presence of pyridine using dry chloroform as solvent with a temperature range of 25-60°C. These acetals [R-C(OMe)2Me] are obtained from the reaction of alkyl methyl ketones with trimethyl orthoformate in the presence of p-toluenesulfonic acid as catalyst in pure methanol as solvent. The new acetylated enol ethers proved to be versatile building blocks for the construction of interesting alkyl trifluoromethyl substituted heterocycles. Thus, examples of isoxazoline, pyrazoline, pyrazole and pyrimidinone have been obtained in good yields (62-79%).
TiCl4-Catalyzed Addition of HN3 to Aldehydes and Ketones. Thermolysis and Photolysis of α-Azido Ethers
Hassner, Alfred,Fibiger, Richard,Amarasekara, Ananda S.
, p. 22 - 27 (2007/10/02)
Aldehydes react with hydrazoic acid and alcohols in the presence of catalytic amounts of TiCl4 to produce α-azido ethers.The conversion of simple ketones to methyl α-azido alkyl ethers can be accomplished by means of hydrazoic acid and methyl orthoformate.Both gas-phase thermolysis and photolysis of representative α-azido ethers were studied and shown to produce mainly imino ethers.In the thermolysis, migratory preference decreases in the series H >> CH3 > Ph >> OR.
Cyclopropylidene Insertion Reactions: 2-Methoxy-1,2-dimethylbicyclobutane
Hamon, David P. G.,Trenerry, Craige V.
, p. 809 - 821 (2007/10/02)
The syntheses of 1,1-dibromo-2-isopropyl-2-metoxy-3,3-dimethylcyclopropane (12), 1,1-dibromo-2-methoxy-2,3,3-trimethylcyclopropane (11), 1,1-dibromo-2-isopropyl-2-methoxycyclopropane (21), 1,1-dibromo-2-methoxy-3,3-dimethylcyclopropane (29) and 1,1-dichloro-2-methoxy-3,3-dimethylcyclopropane (30) are described.The compounds (12), (21) and (29) give rise to alkoxy allenes on treatment with metyllithium in ether.The major product of the reaction of methyllithium with the dibromide (11) is 2-methoxy-1,2-dimethylbicyclobutane (26).This is the first example of this class of compound.Treatment of the compound (30) with methyllithium in the presence of hexamethylphosphoramide gave the homologous allene, 2-methoxy-4-methylpenta-2,3-diene (25).
