- A novel, general method for the synthesis of nitrile oxides: Dehydration of O-silylated hydroxamic acids
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(Formula presented) O-Silylated hydroxamic acids serve as stable, readily accessible, crystalline precursors to nitrile oxides when treated with trifluoromethanesulfonic anhydride and triethylamine. Under these mild conditions in the presence of olefins O
- Muri, Dieter,Bode, Jeffrey W.,Carreira, Erick M.
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p. 539 - 541
(2007/10/03)
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- Synthesis of optically active 4,5-dihydroisoxazolecarboxylic acids
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A series of regioisomers of 4,5-dihydroisoxazolecarboxylates have been synthesized in the 1,3-dipolar intermolecular cycloaddition and subjected to enzymatic hydrolysis by α-chymotrypsin from bovine pancreas (type II) and to microbial hydrolysis by an Aspergillus niger fungus. For some compounds this hydrolysis time led to the obtaining of a racemic mixture, and for others the reaction was enantioselective.
- Zadrozna, Irmina,Kurkowska, Joanna,Makuch, Iwona
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p. 111 - 118
(2007/10/03)
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- Unusual Regioselectivity of the Dipolar Cycloaddition Reactions of Nitrile Oxides and Tertiary Cinnamides and Crotonamides
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Benzonitrile oxides undergo 1,3-dipolar cycloaddition reactions with methyl cinnamate to produce the 5-phenyl and 4-phenyl regioisomers in approximately an 80:20 ratio. However, use of N,N-diethylcinnamide as the dipolarophile unexpectedly resulted in the formation of the 5-phenyl and 4-phenyl regioisomers in a 23:77 ratio. Studies have shown that this phenomena occurs only for tertiary cinnamides. In addition, it has been demonstrated that the phenyl group of tertiary cinnamides is not essential for the reversal of regioselectivity since crotonamides produce the same results and trends as the cinnamides. However, since acrylates and acrylamides both produce the 5-carbonyl regioisomers, it can be concluded that the β-substituent is playing a key role for the unexpected results by possibly increasing steric interactions between the dipole and dipolarophile in the transition state. Transition state energies were calculated for the regioisomeric cycloadduct pairs derived from several crotonamides as well as methyl crotonate. These calculations indicate that steric factors are indeed responsible for the reversal of regioselectivity.
- Weidner-Wells, Michele A.,Fraga-Spano, Stephanie A.,Turchi, Ignatius J.
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p. 6319 - 6328
(2007/10/03)
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- Synthese 'one pot' de derives isoxazoliniques par activation sonochimique
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Several isoxazolines are prepared in biphasic system Ca(OCl2)/CH2Cl2 or NaOCl/CH2Cl2. Yields are increased under sonication when compared to classical stirring in the same conditions.
- Bougrin, Khalid,Lamiri, Mustapha,Soufiaoui, Mohamed
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p. 4455 - 4458
(2007/10/03)
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- THE REACTION OF TRIPHENYLPHOSPHINE WITH ARYLBROMONITROMETHANES. FORMATION OF ARYLNITRILOXIDES
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Formation of furoxans and Δ2-isoxazolines confirms that arylnitriloxides are intermidiates in the reaction of arylbromonitromethanes with triphenylphosphine.
- Coutouli-Argyropoulou, E.
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p. 2029 - 2030
(2007/10/02)
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