Showing papers by "Christian V. Stevens published in 2005"
TL;DR: A multicomponent reaction (MCR) between amines, aldehydes, and isocyanides bearing an acidic alpha-proton gives easy access to a diverse range of highly substituted 2-imidazolines.
Abstract: A multicomponent reaction (MCR) between amines, aldehydes, and isocyanides bearing an acidic α-proton gives easy access to a diverse range of highly substituted 2-imidazolines. The limitations of the methodology seem to be determined by the reactivity of the isocyanide and by the steric bulk on the in situ generated imine rather than by the presence of additional functional groups on the imine. Less reactive isocyanides, for example p-nitrobenzyl isocyanide 25a, react successfully with amines and aldehydes, using a catalytic amount of silver(I) acetate. Some of the resulting p-nitrophenyl-substituted 2-imidazolines undergo air oxidation to the corresponding imidazoles. Differences in reactivity of the employed isocyanides are explained with use of DFT calculations. Difficult reactions with ketones instead of aldehydes as the oxo-compound in this MCR are promoted by silver(I) acetate as well.
141 citations
TL;DR: In a radial hyphal growth bioassay with both plant pathogens, all derivatives showed a higher fungicidal action than chitosan, and the effect of different substitutions is discussed in relation to insecticidal and fungicidal activity.
Abstract: Chitosan, the N-deacetylated derivative of chitin, is a potential biopolysaccharide owing to its specific structure and properties In this paper, we report on the synthesis of 24 new chitosan derivatives, N-alkyl chitosans (NAC) and N-benzyl chitosans (NBC), that are soluble in dilute aqueous acetic acid The different derivatives were synthesized by reductive amination and analyzed by 1H NMR spectroscopy A high degree of substitution (DS) was obtained with N-(butyl)chitosan (DS 036) at a 1:1 mole ratio for NAC derivatives and N-(2,4-dichlorobenzyl)chitosan (DS 052) for NBC derivatives Their insecticidal and fungicidal activities were tested against larvae of the cotton leafworm Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae), the grey mould Botrytis cinerea Pers (Leotiales: Sclerotiniaceae) and the rice leaf blast Pyricularia grisea Cavara (Teleomorph: Magnaporthe grisea (Hebert) Barr) The oral feeding bioassay indicated that all the derivatives had significant insecticidal activity at 5 g kg(-1) in artificial diet The most active was N-(2-chloro-6-fluorobenzyl)chitosan, which caused 100% mortality at 0625 g kg(-1), with an estimated LC50 of 032 g kg(-1) Treated larvae ceased feeding after 2-3 days; the mechanism of action remains unknown In a radial hyphal growth bioassay with both plant pathogens, all derivatives showed a higher fungicidal action than chitosan N-Dodecylchitosan, N-(p-isopropylbenzyl)chitosan and N-(2,6-dichlorobenzyl)chitosan were the most active against B cinerea, with EC50 values of 057, 057 and 052 g litre(-1), respectively Against P grisea, N-(m-nitrobenzyl)chitosan was the most active, with 77% inhibition at 5 g litre(-1) The effect of different substitutions is discussed in relation to insecticidal and fungicidal activity
140 citations
TL;DR: A series of O-(acyl) chitosan derivatives with a degree of substitution (DS) between 002 and 028 were synthesized by reaction of alkanoic acid derivatives with chitoshan in the presence of H2SO4 as a catalyst as discussed by the authors.
Abstract: A series of O-(acyl) chitosan (OAC) derivatives with a degree of substitution (DS) between 002 and 028 were synthesized by reaction of alkanoic acid derivatives with chitosan in the presence of H2SO4 as a catalyst The reaction was performed at 80 °C for 4 h with different mol ratios of alkanoic acids to chitosan The synthesized compounds were analyzed by 1H- and 13C-NMR spectroscopy A high DS was obtained with O-(butyroyl) chitosan (DS 028) at a mol ratio of (1:5) chitosan to butyric acid Their fungicidal activity against the grey mould Botrytis cinerea (Leotiales: Sclerotiniaceae) and the rice leaf blast pathogen Pyricularia grisea (Teleomorph: Magnaportha grisea) has been evaluated O-(decanoyl) chitosan at mol ratio of 1:2 (chitosan to decanoic acid) was the most active compound against B cinerea (EC50=102 gl-1) and O-(hexanoyl) chitosan displayed the highest activity against P grisea (EC50=111 gl-1) It has been mentioned that some derivatives also repressed spore formation at rather high concentrations (10, 20 and 50 gl-1) The insecticidal activity has been screened at 5 gkg-1 artificial diet against the larvae of the cotton leafworm Spodoptera littoralis (Lepidoptera: Noctuidae) The results revealed that all of the synthesized derivatives showed high inhibition of growth of the larvae of S littoralis compared to chitosan (7% growth inhibition) and the most active one was O-(decanoyl) chitosan (64% growth inhibition) after 5 days of feeding on treated artificial diet
74 citations
43 citations
TL;DR: The halogen atom transfer radical cyclization (HATRC) has been evaluated on N-(indolylmethyl)trichloroacetamides under Cu(I)Cl catalysis using nitrogen containing ligands.
31 citations
TL;DR: In this article, a new protocol for pyrrole synthesis was developed by a unique one-pot combination of ring-closing metathesis and in situ oxidative aromatization by a quinone.
Abstract: A new and straightforward protocol for pyrrole synthesis is developed by a unique one-pot combination of ring-closing metathesis and in situ oxidative aromatization by a quinone.
24 citations
TL;DR: In this paper, N-Boc protected pyroglutamates with strong bases lead to a Boc migration from the N-atom to the C2 position when no or poor electrophiles are being used.
19 citations
TL;DR: Inulin, a polydisperse reserve polysaccharide from chicory, was chemically modified via alkoxylation using ethylene oxide, in a water free medium resulting in a range of products with very distinct properties, such as a highly increased water solubility, moderate surface-active properties and high cloud points in electrolyte media.
17 citations
TL;DR: It was shown that in S. littoralis methanoproline itself did not show any significant activity but that derivatives 5, 7, 8, and 10 did show a reasonable repulsive/antifeedant activity that was comparable to the commercial repellent DEET.
Abstract: 2,4-Methanoproline is a natural product isolated from the seeds of Ateleia herbert smithii Pittier that was formerly suggested to have insect repellent/antifeedant activity; however, this was not tested quantitatively. In this study the insect repellent/antifeedant potency of methanoproline was measured against larvae of the cotton leafworm, Spodoptera littoralis (Boisd.), and adults of the cowpea weevil, Callosobruchus maculatus (F.). In addition, several N-alkyl, amino, and nitrile derivatives of methanoproline with varying stereodemanding substituents were synthesized and also tested. It was shown that in S. littoralis methanoproline itself did not show any significant activity but that derivatives 5, 7, 8, and 10 did show a reasonable repulsive/antifeedant activity that was comparable to the commercial repellent DEET. A significant repellent activity was scored for methanoproline in adults of C. maculatus that was similar to DEET. Keywords: 2,4-Methanoproline; Ateleia herbert smithii; insect repellent...
16 citations
TL;DR: A short and elegant synthetic pathway was developed for the synthesis of 1,3-dioxo-hexahydropyrido[1,2-c][1,3]diazepine carboxylates, a new 1, 3-diazepan-2,4-dione containing bicyclic moiety, starting from pyroglutamate esters.
13 citations
TL;DR: A new one-step protocol was developed, comprising N-carbamoylation using an isocyanate followed by intramolecular ring expansion that provides a straightforward access to this interesting seven-membered skeleton.
Journal Article•
TL;DR: The regioselectivity of the addition is explained by reversal of polarization of the azadiene due to the electron-withdrawing character of the halogenated phenyl substituents.
Abstract: Several 1-phosphono-2-aza-1,3-butadienes, 1 and 13−20, were evaluated in the reaction with different enolate-type nucleophiles to induce addition at the 1- or the 4-position of the azadiene. 1-Phosphono-2-azadienes 1 react with sodium malonate at the 1-position, leading to the formation of bisenamines 12 after elimination of the phosphonate moiety. On the contrary, sodium malonate adds at the 4-position of 1-aryl-1-phosphono-2-azadienes 14−19 when the azadienes bear a halogenated phenyl substituent, and the resulting addition products 21−26 are easily transformed into the corresponding phosphonylated γ-lactams 35−40. The regioselectivity of the addition is explained by reversal of polarization of the azadiene due to the electron-withdrawing character of the halogenated phenyl substituents.
Journal Article•
TL;DR: Chitosan is a new functional material with high potential in various fields, such as environmental and biomedical engineering, and is prepared by the alkaline deacetylation of chitin obtained from crab shells.
Abstract: -glucose, and is prepared by the alkaline deacetylation of chitin obtained from crab shells. Chitosan has become of great interest not only as an underutilized resource, but also as a new functional material with high potential in various fields, such as environmental and biomedical engineering (Dodane and Vilvalam, 1998 and Rabea
TL;DR: Using the microreactor system, the scale-up problems were avoided and large amounts of α-aminophosphonates could be generated in a short time, and similar yields and purities were obtained compared to the batch reaction.
Abstract: The synthesis of α-aminophosphonates on a large scale is not always straightforward One of the described methodologies has now been adjusted for use in a microreactor system The CPC College System was used to investigate the continuous production of α-aminophosphonates This technology couples miniaturisation to optimal reaction conditions for the production of chemical and pharmaceutical intermediates The reaction of an imine with a dialkyl phosphite in different solvents was optimised, since the use of a solvent is necessary when using a microreactor When methanol was used, a considerable reduction of the reaction time was noticed in comparison with other commonly used solvents Subsequently, several reaction parameters were optimised in batch and compared with the continuous process in the microreactor Similar yields and purities were obtained compared to the batch reaction Using the microreactor system, the scale-up problems were avoided and large amounts of αaminophosphonates could be generated in a short time
TL;DR: 4-Phosphono-β-lactams are synthesized via a three-step sequence, including final formation of the C3-C4 bond through a phosphorus-stabilized carbanion, which results in good yields and ease of reaction.
Abstract: 4-Phosphono-β-lactams are synthesized via a three-step sequence, including final formation of the C3-C4 bond through a phosphorus-stabilized carbanion. The chlorinated precursors can be synthesized via two different methods: a one-pot N-acylation of an aromatic imine followed by addition of a trialkyl phosphite or phosphonylation of a suitable imine followed by N-acylation in a separate reaction step. The former method was preferred because of the ease of the reaction and the good yields obtained.
TL;DR: In this paper, a straightforward pyrrole synthesis from diallylamines is developed by using a tandem catalyst system leading to ring-closing metathesis with the second generation Grubbs' catalyst (10%) followed by dehydrogenation in the presence of RuCl 3 ǫ×H 2 O (2%).
Abstract: A straightforward pyrrole synthesis from diallylamines is developed by using a tandem catalyst system leading to ring-closing metathesis with the second generation Grubbs’ catalyst (10%) followed by dehydrogenation in the presence of RuCl 3 × H 2 O (2%).
Journal Article•
Journal Article•
TL;DR: Chitosan of low molecular weight (made from crab shells, 85% degree of deacetylation, DDA) and aldehydes were purchased from Sigma-Aldrich Co. and NAC derivatives were synthesized ac-cording to Kim.
Abstract: Chitosan of low molecular weight (made from crab shells, 85% degree of deacetylation, DDA) and aldehydes were purchased from Sigma-Aldrich Co. (Bornem, Belgium). Soybean-wheat germ insect artificial diet was purchased from Stonefly Ind. (Bryan, TX, USA). NAC derivatives were synthesized ac-cording to Kim
TL;DR: In this paper, a straightforward synthesis of new cis-4-aryl-3-chloro-2-azetidinones was developed, using a halogen-lithium exchange reaction on 4-aryl 3,3-dichloro-1,2-hexadecane.
Abstract: A straightforward synthesis of new cis-4-aryl-3-chloro-2-azetidinones was developed, using a halogen-lithium exchange reaction on 4-aryl-3,3-dichloro-2-azetidinones. This methodology was further extended to the use of alkyl halides as electrophiles, while more complex electrophiles could not be introduced.
TL;DR: In this article, N-Boc protected pyroglutamates with strong bases lead to a Boc migration from the N-atom to the C2 position when no or poor electrophiles are being used.
Abstract: Treatment of N-Boc protected pyroglutamates with strong bases lead to a Boc migration from the N-atom to the C2 position when no or poor electrophiles are being used.
01 Jan 2005
TL;DR: An overview of the existing entries to alkenes, geminally substituted with both a halogen and a heteroatom other than a chalcogen, can be found in this paper.
Abstract: An overview is presented of the hitherto reported entries to alkenes, geminally substituted with both a halogen and a heteroatom other than a halogen or a chalcogen. The covered methodologies have been categorized according to the chemical class of the precursor molecule and the nature of the transformation yielding the gem -difunctionalized alkene. This work discusses primary literature reports up to the end of 2012.
TL;DR: In this article, a new one-step protocol was developed, comprising N-carbamoylation using an isocyanate followed by intramolecular ring expansion, which provided a straightforward access to this interesting seven-membered skeleton.
Abstract: [reaction: see text] Perhydro-1,3-diazepine-2,4-diones are rare and can only be prepared, up to now, by special methods. A new one-step protocol was developed, comprising N-carbamoylation using an isocyanate followed by intramolecular ring expansion. This new methodology provides a straightforward access to this interesting seven-membered skeleton.