Konevenagel Reaction. Kinetic study of the reaction of (+)-3-methyl-cyclohexanone with malononitrile

Abstract

The condensation of malononitrile with (+ )-3-methylcyclohexanone produced an 80-85% yield of ( -)-3methylcyclohexylidenemalononitrile. The reaction, followed polarimetrically in alcohol-water, is kinetically second order and efficiently catalyzed by weak bases ( -amino acids, cyclic amino acids, NBuOAc), furnishing solutions having an apparent pH of 7.5-8.0. With /3-alanine as catalyst, the £a was 7.6 kcal/mol compared to 11 kcal/mol uncatalyzed. Stronger bases (barbital, NaOAc, KOAc, KF, piperidine) effected more rapid condensation but poorer kinetics because of telemerization of malononitrile at the higher pHs.

Synthesis and Catalytic Properties of Hybrid Mesoporous Materials Assembled from Polyhedral and Bridged Silsesquioxane Monomers

“…50. 51 The kinetics of the Knoevenagel reactions have been widely studied, and the process follows first‐order kinetics with respect to each reactant and catalyst 52–54. Moreover, Knoevenagel reactions have been used as test reactions to determine the number and strength of basic sites.…”

“…[50,51] The kinetics of the Knoevenagel reactions have been widely studied, and the process follows first-order kinetics with respect to each reactant and catalyst. [52][53][54] Moreover, Knoevenagel reactions have been used as test reactions to determine the number and strength of basic sites. Thus, we performed the Knoevenagel condensation between benzaldehyde and substrates with different pK a values (with distinct activated methylenic groups), such as malononitrile (pK a % 7), ethyl cyanoacetate (pK a % 9), and ethyl acetoacetate (pK a % 11), in the presence of the hybrid mesoporous material HYB-75P-25B (Table 3).…”

Enantiomerically Pure β-Amino Acids: A Convenient Access to Both Enantiomers of trans-2-Aminocyclohexanecarboxylic Acid

“…[7] The published syntheses of enantiomerically pure 2 or ent-2 are based on the following sequence (Scheme 1): (i) preparation of the racemic amino acid rac-2 by alkali metal reduction of anthranilic acid 1, (ii) N-benzoylation to rac-3, (iii) separation of the enantiomers either by using (Ϫ)-quinine as the chiral auxiliary or by induced crystallization, (iv) N-debenzoylation, (v) introduction of an N-protecting group suitable for peptide synthesis, such as BOC (Scheme 1). [5,8,9] In our hands, the reduction of 1 proved tedious and relatively low-yielding (10Ϫ30%). The isolation of pure rac-3 from the benzoylation requires intermediate esterification, column chromatography and hydrolysis.…”

“…For the ee determination, a sample of 5 (or ent-5) was converted into the dimethyl ester by treatment with an ethereal solution of diazomethane and analyzed by GC on a 25 m WCOT FS CP-Chiralsil-Dex CB column. C 8 [13] [α] 25 D ϭ Ϫ18.5 (c ϭ 1.00, acetone)}.…”

Synthesis and biological evaluation of (acyl)hydrazones and thiosemicarbazones obtained via in situ condensation of iminium salts with nitrogen-containing nucleophiles

“…Iminium salts are key reactive synthons involved in important organic reactions [1][2][3][4][5][6] that lead to the formation of C-C bonds. In previous studies [7], we reported the preparation of the iminium chlorides of cyclic (thio)ureas through the condensation of the atypical Vilsmeier reagent I and the imidazolidin-2-(thio)one substrates (Fig.…”