Search results for "cyclic"

Synthesis and Photoluminescent Properties of 1,1‘-Binaphthyl-Based Chiral Phenylenevinylene Dendrimers

2003

New chiral, soluble binaphthyl derivatives that incorporate stilbenoid dendrons at the 6,6′-positions have been prepared. The synthesis of the new enantiopure dendrimers was performed in a convergent manner by Horner-Wadsworth-Emmons (HWE) reaction of the appropriately functionalized 1,1′-binaphthyl derivative (R)-1 and the appropriate dendrons (R)2nGn-CHO. Different electroactive units were incorporated in the peripheral positions of the dendrons in order to tune both the optical and electrochemical behavior of these systems. Fluorescence measurements on the chiral dendrimers reveal a strong emission with maxima between 409 and 508 nm depending upon the substitution pattern. Finally, t…

Effect of auxin on the mitotic cell cycle in cultured leaf segments at different stages of development in wheat

1987

Young leaves of Triticum timopheevi Zukh. show a defined gradient of development. One-mm-long sections from such leaves were cultured in vitro. At a low concentration of exogenous auxin, cells in the most basal, highly meristematic explants divided readily in culture, but in the absence of auxin they soon ceased dividing and were arrested in G1 and G2 of the mitotic cell cycle. In the region adjoining the meristem, where most cells were arrested in G1, very high concentrations of auxin had to be applied to reinitiate cell division, i.e. stimulate transitions from G1 to S-phase and from G2 to mitosis. Above this potentially auxin-responsive region, which represented less than 50% of the tota…

Direct observation and thermal transformations of dications derived from dibenzotropylium ions

1992

Abstract Carboxylic acid 1 and its derivatives 2 , 3 treated with triflic acid below −20°C afford the dications 1H 2+2- 3H 2+2. Cyclodehydration above 20°C (or in the gas-phase, CIMS of 3 ) leads to the diprotonated ketone 4H 2+2.

Stereoselective Synthesis and Structural Correction of the Naturally Occurring Lactone Stagonolide G

2010

A convergent synthesis of the structure proposed for the naturally occurring lactone stagonolide G is described. All three stereocenters were created with the aid of asymmetric Brown allylations. The lactone ring was built by means of a ring-closing metathesis (RCM). The synthetic and the natural compound differed in their spectral properties. A new structure is now proposed for stagonolide G and demonstrated by means of a chemical transformation.

Macrocyclic peptides in anionic polymers of amino acid N-carboxylic anhydrides.

1976

Makrobicyclische Endorezeptoren: Synthese, Kristallstruktur und Einschluß organischer Gastmoleküle

1992

Macrobicyclic Endoreceptors: Synthesis, Crystal Structure, and Inclusion of Organic Guests The macrobicyclic ligand 2 is synthesized in a one-step cyclization procedure. According to an X-ray structure analysis three dichloromethane guest molecules are included inside the cavity, whereas water and methanol are found outside the cavity. The rigid endo preorganization of the nitrogen donors allows the complexation of three 2,9-disubstituted 1,10-phenanthrolines inside the cavity.

Electrochemical study on (NN)Fe3 (CO)9 ((NN) = 2,3-diazanorbornene) and related compounds. A new example of activation of carbon monoxide replaceme…

1985

Abstract The compound (NN)Fe 3 (CO) 9 ( 1 ) in tetrahydrofuran undergoes two reversible one-electron reduction processes in cyclic voltammetry at the platinum electrode. A rapid electron transfer-catalyzed reaction occurs when 1 is reduced in the presence of L (L = P(OMe) 3 ) and this gives (NN)Fe 3 (CO) 8 L ( 2 ), quantitatively. Only an electron-induced nucleophilic substitution is observed for compound 2 under the same conditions, yielding (NN)Fe 3 (CO) 7 L 2 , which undergoes a similar reaction but with much lower efficiency, to give (NN)Fe 3 (CO) 6 L 3 .

Double and triple calix[4]arenis connected via the oxygen functions

1990

New macrocyclic molecules are described containing two or three p-tert-butylcalix[4]arene subunits connected via their oxygen atoms. These macrocycles are available by two general methods which are capable of producing assemblies with bridges of varying rigidity and length.

N-[3-(5-Oxo-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-2-ylamino)phenyl]furan-3-carboxamide

2010

In the title compound, C26H20N2O3, the two aromatic rings of the tricyclic unit are oriented at a dihedral angle of 54.53 (9)°. The crystal structure displays intermolecular N—H...O hydrogen bonding.

Lewis Acid-Catalyzed Stereoselection on Carbohydrate Templates

1989

The chirality and the complexing abilities of carbohydrates are utilized for chemical stereoselection in different reactions. In this sense, the carbohydrates are investigated as the chiral auxiliaries in alkylation reactions and in Michael additions of ester enolates. Furthermore, carbohydrates are demonstrated to be efficient chiral matrices in Lewis acid-catalyzed Diels-Alder reactions. They also effect stereoselection in a new synthesis of β-branched carboxylic acid derivatives. O-Acylated glycosylamines are shown to be potent chiral templates in the Strecker synthesis and in the Ugi four-component condensation to give α-amino acid derivatives in high yield and diastereoselectivity. In …