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13 pages, 1501 KiB

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A Small Change in Structure, a Big Change in Flexibility

by Nikolay G. Vassilev and Ivo C. Ivanov

Molecules 2023, 28(24), 8004; https://doi.org/10.3390/molecules28248004 - 8 Dec 2023

Cited by 4 | Viewed by 1812

Studies of the rotational barrier energy of the amide bond using quantum computing and nuclear magnetic resonance (NMR) are focused mainly on its use as a model of the peptide bond. The results of these studies are valuable not only in terms of [...] Read more.

Studies of the rotational barrier energy of the amide bond using quantum computing and nuclear magnetic resonance (NMR) are focused mainly on its use as a model of the peptide bond. The results of these studies are valuable not only in terms of the fundamental conformational properties of amide bonds, but also in the design of molecular machines, which have recently attracted interest. We investigate the fluxionality of the amide and enamide bonds of compound 3-[(E)-(dimethylamino)methylidene]-1,1-dimethylurea using advanced dynamic NMR experiments and a theoretical evaluation of the density functional theory (DFT) calculation. The dynamic NMR study shows restricted rotation around the amide group (16.4 kcal/mol) and a very high barrier around the enamine group (18.6 kcal/mol). In a structurally similar compound, (E)-3-(dimethylamino)-N,N-dimethylacrylamide (N atom is replaced by CH), the amide barrier is 12.4 kcal/mol and the enamine barrier is 11.7 kcal/mol. The DFT studies of both compounds reveal the electronic origin of this phenomenon. Theoretical calculations reveal the origin of the higher enamine barrier. The better delocalization of the lone pair of electrons on the end nitrogen atom into the antibonding orbital of the neighboring C–N double bond leads to the better stabilization of the ground state, and this leads to a greater increase in the enamine barrier. Full article

(This article belongs to the Section Organic Chemistry)

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5 pages, 158 KiB

Open AccessArticle

Convenient Replacement of the Hydroxy by an Amino Group in 4 Hydroxycoumarin and 4-Hydroxy-6-methyl-2-pyrone under Microwave Irradiation

by Edmont V. Stoyanov and Ivo C. Ivanov

Molecules 2004, 9(8), 627-631; https://doi.org/10.3390/90800627 - 31 Jul 2004

Cited by 24 | Viewed by 10160

Abstract

The reaction of 4-hydroxycoumarin (1) with some primary amines 2a-h and morpholine (2i) under microwave irradiation occurred without opening of the lactone ring to give N-substituted 4-aminocoumarins 3a-i in excellent yields. Under the same experimental conditions, 4-hydroxy-6-methyl-2-pyrone (4) reacted with benzylamine (2e) or [...] Read more.

The reaction of 4-hydroxycoumarin (1) with some primary amines 2a-h and morpholine (2i) under microwave irradiation occurred without opening of the lactone ring to give N-substituted 4-aminocoumarins 3a-i in excellent yields. Under the same experimental conditions, 4-hydroxy-6-methyl-2-pyrone (4) reacted with benzylamine (2e) or 2-phenyl- ethylamine (2f) to give the corresponding N,N'-disubstituted 4-amino-6-methyl-2-pyridones 5e,f. The main advantages of this procedure are dramatically shortened reaction times, higher amine utilization and considerably improved yields. Full article

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1 pages, 121 KiB

Open AccessShort Note

4-Morpholino-2-oxo-2H-chromene-3-carbaldehyde

by Boyan I. Iliev and Ivo C. Ivanov

Molecules 2001, 6(6), M218; https://doi.org/10.3390/M218 - 25 May 2001

Cited by 3 | Viewed by 3714

Abstract

The title compound 3 has been allegedly prepared earlier [1] by refluxing the same starting materials 1 and 2 in ethanol for 10 min. Full article

(This article belongs to the Section Molbank Section of Molecules, 1997-2001)

1 pages, 119 KiB

Open AccessShort Note

(+)-(1R)-N¹-{[(1R,1S)-2-Oxocyclohexyl]methyl}-1-phenyl-1-ethanaminium Chloride

by Edmont V. Stoyanov and Ivo C. Ivanov

Molecules 2001, 6(6), M217; https://doi.org/10.3390/M217 - 25 May 2001

Viewed by 3114

Abstract

The Mannich bases of cyclohexanone with benzylamine and 3,4-methylenedioxybenzylamine hydrochlorides have been prepared in moderate yields using aqueous formaldehyde solution [1].[...] Full article

(This article belongs to the Section Molbank Section of Molecules, 1997-2001)

1 pages, 115 KiB

Open AccessShort Note

(R,S)-N-[(2-Oxocyclohexyl)methyl]-2-phenyl-1-ethanaminium Chloride

by Edmont V. Stoyanov and Ivo C. Ivanov

Molecules 2001, 6(6), M216; https://doi.org/10.3390/M216 - 25 May 2001

Viewed by 3387

Abstract

The Mannich bases of cyclohexanone with benzylamine and 3,4-methylenedioxybenzylamine hydrochlorides have been prepared in moderate yields using aqueous formaldehyde solution [1].[...] Full article

(This article belongs to the Section Molbank Section of Molecules, 1997-2001)

1 pages, 113 KiB

Open AccessShort Note

(R,S)-N-[(2-Oxocyclohexyl)methyl]-1-butanaminium Chloride

by Edmont V. Stoyanov and Ivo C. Ivanov

Molecules 2001, 6(6), M215; https://doi.org/10.3390/M215 - 25 May 2001

Viewed by 3732

Abstract

The Mannich bases of cyclohexanone with benzylamine and 3,4-methylenedioxybenzylamine hydrochlorides have been prepared in moderate yields using aqueous formaldehyde solution [1].[...] Full article

(This article belongs to the Section Molbank Section of Molecules, 1997-2001)

1 pages, 88 KiB

Open AccessShort Note

4-Hydroxy-6-methyl-3-nitroso-1-phenethyl-2(1H)-pyridinone

by Edmont V. Stoyanov and Ivo C. Ivanov

Molecules 2000, 5(1), M132; https://doi.org/10.3390/M132 - 24 Jan 2000

Viewed by 3041

Abstract

The starting 4-hydroxy-6-methyl-1-phenethyl-2(1H)-pyridinone (1) was prepared according to the known procedure [1,2].[...] Full article

(This article belongs to the Section Molbank Section of Molecules, 1997-2001)

14 pages, 65 KiB

Open AccessArticle

General Method for the Preparation of Substituted 2-Amino-4H,5H-pyrano[4,3-b]pyran-5-ones and 2-Amino-4H-pyrano[3,2-c]pyridine-5-ones

by Edmont V. Stoyanov, Ivo C. Ivanov and Dieter Heber

Molecules 2000, 5(1), 19-32; https://doi.org/10.3390/50100019 - 21 Jan 2000

Cited by 69 | Viewed by 8905

Abstract

Reaction of 4-hydroxy-6-methyl-2-pyrone (1a) as well as 4-hydroxy-6-methyl-2(1H)-pyridones (1b-d) with arylmethylene malononitriles or arylmethylene methyl cyanoacetates (2a-h) leads to the formation of the very stable 5,6-fused bicyclic 2-amino-4Hpyran derivatives 3a-3af. Full article

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2 pages, 96 KiB

Open AccessShort Note

N-{2-[(2-Oxo-2H-chromen-4-yl)amino]ethyl}acetamide

by Stoyan K. Karagiosov, Ivo C. Ivanov and Boyan I. Iliev

Molecules 1999, 4(12), M126; https://doi.org/10.3390/M126 - 17 Dec 1999

Cited by 4 | Viewed by 3436

Abstract

The direct synthesis of 4-(monoalkylamino)coumarins from primary amines [1] was developed on the basis of the reaction of 4-hydroxycoumarin with ammonium acetate in acetic acid as reported by Joshi et al. [2].[...] Full article

(This article belongs to the Section Molbank Section of Molecules, 1997-2001)

2 pages, 91 KiB

Open AccessShort Note

6-Methyl-3-nitroso-1-phenethyl-4-(phenethylamino)-2(1H)-pyridinone

by Edmont V. Stoyanov and Ivo C. Ivanov

Molecules 1999, 4(12), M125; https://doi.org/10.3390/M125 - 17 Dec 1999

Viewed by 2908

Abstract

In the course of our recent studies on the reactivity of some 4-amino-2-pyridones [1-3] we accomplished the nitrosation of the N,N-disubstituted 4-amino-2-pyridone 2.[...] Full article

(This article belongs to the Section Molbank Section of Molecules, 1997-2001)

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