Search results for "cyclic"

Synthetic studies toward natural furanosesquiterpenoids from santonin. Synthesis of (+)-1,2-dihydrotubipofuran

1994

Abstract Santonin (1) was converted into (+)-1,2-dihydrotubipofuran (13) via a synthetic pathway involving a very easy preparation of 7,11-ene-8,12-olide and 8,12-furan moieties and A-ring elaboration on the eudesmane framework.

Iod-induzierte stereoselektive Carbocyclisierungen – Beispiele für eine breit anwendbare, neue Methode zur Synthese von Cyclohexan- und -hexen-Deriva…

1988

Studien zum Vorgang der Wasserstoffübertragung, 52. Zur Kenntnis der elektroreduktiven Spaltung der N - N-Bindung

1978

Am Beispiel von 35 Hydrazinderivaten wird die elektroreduktive Spaltung polarographisch und praparativ untersucht. Es wurde gefunden: 1) Beim mono-, tri- und tetrabenzoylierten Hydrazin 9, 11 bzw. 12 verschiebt sich das Potential proportional der Anzahl der Benzoylgruppen nach positiveren Werten. Beim symmetrischen 1,2-Dibenzoylhydrazin (10) wird das Halbstufenpotential E1/2 — bedingt durch H-Verbruckung und mesomere Stabilisierung — stark nach negativen Werten verschoben. — 2) Bei den cyclischen Hydrazinderivaten 14–16 werden die E1/2-Werte sowohl in Abhangigkeit von der Ringspaltung als auch durch cis-Fixierung der Benzoylgruppen noch zusatzlich nach positiveren Werten verlagert. — 3) Ube…

Efficient Synthesis of 1,4,7-Triazacyclononane and 1,4,7-Triazacyclononane-Based Bifunctional Chelators for Bioconjugation

2014

The reaction of diethylenetriamine with chloroacetaldehyde yielded a bicyclic aminal intermediate for the synthesis of 1,4,7-triazacyclononane (TACN), a macrocyclic polyamine the derivatives of which find applications as catalysts, bleaching agents, and chelators for medical imaging. This new synthetic protocol outperforms the synthetic methods described so far because it does not involve any cyclization step. Moreover, this aminal intermediate allowed access to a new family of TACN derivatives functionalized on the carbon skeleton, for example, C-aminomethyl-TACN. This novel compound is a precursor of valuable bifunctional chelating agents for nuclear medicine, in particular, for the prepa…

Isolation, separation and quantification of metabolites of the carcinogenic polycyclic aromatic hydrocarbon dibenz(a,h)anthracene

1986

Time-dependent monomerization of gramicidin A, enhanced by phosphatidylcholine in non-polar solvents

1986

Abstract The usefulness of size-exclusion high-performance liquid chromatography for the study of gramicidin A dimer—monomer conformational equilibrium in non

Fluoride Ion Receptors: A Comparison of a Polyammonium Monocycle Versus its Bicyclic Corollary

2001

Two polyammonium macrocyclic receptors, the monocyclic 3,6,9,17,20,23-hexaazatricyclo [23.3.1.111,15]triaconta-1(29), 11,13,15(30),25,27-hexaene (L1) and its bicyclic analog 1,4,12,15,18,26,31,39-o...

Cyclocondensation of alpha-aminonitriles and enones: a short access to 3,4-dihydro-2H-pyrrole 2-carbonitriles and 2,3,5-trisubstituted pyrroles.

2009

The reaction of alpha,beta-unsaturated carbonyl compounds with aminoacetonitrile hydrochloride furnishes 3,5-disubstituted 3,4-dihydro-2H-pyrrole-2-carbonitriles in a one-pot reaction sequence. While these products can serve as starting materials for the preparation of polysubstituted pyrrolizidines, they are kinetically stable against the base-induced elimination of HCN. In contrast, their 2-substituted analogues obtained from alpha-substituted alpha-aminonitriles can be readily converted to the corresponding 2,3,5-trisubstituted pyrroles under microwave irradiation. The key step presumably involves the thermal electrocyclization of a stabilized 2-azapentadienyl anion formed by condensatio…

Synthesis and NMR configurational study of imidazo[2,1-b]thiazoles from 1H-1,4-diazepine-7(6H)-thiones

1993

Abstract A thermal intramolecular cyclization of 1-vinyl2,3-dihydro-3 H -imidazole-2-thiones to imidazo[2,1-b]thiazoles is reported. A heteronuclear correlation study of these systems was made in order to establish the configuration of the products.

Electrophilic substitution and cyclization of 2,2′-bis(N-methylindolyl): A simple access to potential protein kinase C inhibitor

1994

A strategy is described for the synthesis of functionalized and cyclized 2,2′-bisindolyl derivatives related to several basic systems of natural products. The starting 2,2′-bis(N-methylindolyl) (8) reacts with a variety of electrophiles and electrophilic dienophiles to furnish the novel, functionalized and cyclized bisindolyl derivatives 9–16. In addition, some reactivity and structural aspects are discussed; an X-ray crystallographic analysis of the 2,2′-bisindolyl 8 provided valuable information for the conformational analyses.