Search results for "lactam"

Straightforward Stereoselective Access to Cyclic Peptidomimetics

2009

The preparation of cyclic dipeptide mimetics from chiral imino lactones derived from (R)-phenylglycinol is described. Key steps of the synthetic route included the fully stereoselective construction of a quaternary center, the formation of six-, seven-, or eight-membered lactams by means of an RCM cyclization, and the introduction of a new amino group within the lactam ring. The synthesis of a tripeptide mimetic is also reported.

Synthesis of Highly Functionalized Cyclopentanes as Precursors of Hydroxylated Azidocarbonucleosides

2009

Regio- and stereoisomers of functionalized azido amino alcohols with a cyclopentane skeleton were synthesized in enantiomerically pure forms. Enzymatic ring cleavage of racemic 2-azabicyclo[2.2.1]hept-5-en-3-one gave the corresponding amino acid and one enantiomer of the lactam stereospecifically. These were protected by esterification and carbamoylation, and then epoxidized. The resulting oxiranes underwent cleavage by sodium azide with complementary stereoselectivities. The regioisomeric products were easily separated by crystallization or column chromatography.

Understanding the mechanism of the N-heterocyclic carbene-catalyzed ring-expansion of 4-formyl-β-lactams to succinimide derivatives

2009

The mechanism of the N-heterocyclic carbene (NHC)-catalyzed ring-expansion of 4-formyl-β-lactams to succinimides has been studied using DFT methods at the B3LYP/6-31G∗∗ level. The first step is the nucleophilic attack of NHC to the aldehyde to yield the zwitterionic intermediate, which by a proton-transfer process affords the Breslow intermediate. The lactam N–C breaking bond in this intermediate yields an enol-amidate, which by a keto–enol type equilibrium becomes the ketone form. The subsequent ring-closure achieved by the nucleophilic attack of the amidate to carbonyl carbon allows the formation of the five-membered ring. Finally, elimination of NHC affords the succinimide. Analysis of t…

Influence of processing conditions on some properties of anionically synthesized polycaprolactam in presence of lithium chloride

1980

Nylon 6–LiCl systems of various concentrations were prepared by anionic polymerization of caprolactam in the presence of salt. A depression of both crystallization rate and melting temperature was evidenced through x-ray, density, and DSC analyses. Such a preliminary characterization allowed for choosing the proper conditions in order to obtain amorphous fibers from a spinning operation which was performed at a temperature lower than the pure polymer melting point. These results are of technological relevance, especially in view of obtaining, as in similar cases, large amorphous orientations through a spinning–drawing process and high-modulus fibers after subsequent crystallization. Also, t…

Rheological characterization of polycaprolactam anionically synthesized in the presence of lithium chloride

1980

Melt viscosity and dynamic-mechanical data are reported for samples obtained by anionic polymerization of caprolactam, in the presence of LiCl. The full body of results is essentially in line with those previously reported relative to mixtures of inorganic salts and commercial nylon 6, In particular a drastic-decrease of the melting point and of the rate of crystallization is confirmed as well as an increase of the glass transition temperature and of the melt viscosity. Some quantitative differences exist, which may be attributed to the different molecular weight distribution in the polymers employed in the present work.

Chemodiscrimination of Olefin Bonds Through Cross‐Metathesis Reactions – Synthesis of Functionalized β‐Lactam and β‐Amino Acid Derivatives

2019

A novel and selective fluoride opening of aziridines by XtalFluor-E. synthesis of fluorinated diamino acid derivatives.

2015

The selective introduction of fluorine onto the skeleton of an aminocyclopentane or cyclohexane carboxylate has been developed through a novel and efficient fluoride opening of an activated aziridine ring with XtalFluor-E. The reaction proceeded through a stereoselective aziridination of the olefinic bond of a bicyclic lactam and regioselective aziridine ring opening with difluorosulfiliminium tetrafluoroborate with the neighboring group assistance of the sulfonamide moiety to yield fluorinated diamino acid derivatives. The method based on the selective aziridine opening by fluoride has been generalized to afford access to mono- or bicyclic fluorinated substances.

Synthesis of pyrido[2,3-d]pyrimidines in the reaction of 6-amino-2,3-dihydro-2-thioxo-4(1H)-pyrimidinone with chalcones

1992

6-Amino-2,3-dihydro-2-thioxo-4(1H)-pyrimidinone (1) reacts in boiling DMF with α,/β-unsaturated ketones 2 yielding the pyrido[2,3-d]pyrimidine systems 5 and 6, respectively. The orientation in the addition process can be determined by nmr measurements, especially by NOE difference spectroscopy. The products do not correspond to a normal Skraup or Doebner-v. Miller synthesis.

3-(4-Fluorophenyl)-4-(4-pyridyl)quinolin-2(1H)-one

2006

The title compound, C20H13FN2O, has the quinolin-2(1H)-one unit in the lactam form. The mol­ecules form rows along the b axis via N—H⋯N hydrogen bonds

1963

Es wird gezeigt, das sich e-Caprolactam mit wasserfreiem Bromwasserstoff kationisch polymerisieren last und die dabei gebildeten Polymeren die Struktur von N-(Poly-e-aminocaproyl)-caprolactamen besitzen. Die charakteristische Diacylimidstruktur wird IR-spektroskopisch, durch die Hydroxamsaurereaktion und durch alkoholytische Abspaltung des C-terminalen Lactamringes nachgewiesen. Oligomerengemische, die durch kurzzeitige Umsetzung molarer Mengen an Caprolactam und Initiator bei 175–200°C erhalten werden, konnen durch Hochspannungspapierelektrophorese in einheitliche Individuen aufgetrennt werden. Die Umsetzung mit Hydroxylamin fuhrt zu Oligo-e-aminocapronhydroxamsauren, die sich mit Hilfe au…