Abstract:The fabrication and characterization of continuously tunable, solution-processed distributed feedback (DFB) lasers in the visible regime is reported. Continuous thin film thickness gradients were achieved by means of horizontal dipping of several conjugated polymer and blended small molecule solutions on cm-scale surface gratings of different periods. We report optically pumped continuously tunable laser emission of 13 nm in the blue, 16 nm in the green and 19 nm in the red spectral region on a single chip respectively. Tuning behavior can be described with the Bragg-equation and the measured thickness profile. The laser threshold is low enough that inexpensive laser diodes can be used as pump sources. Weimann, J. Wang, and P. Hinze, "Laser threshold reduction in an all-spiro guest-host system," Appl. Phys. Lett. 85(10), 1659-1661 (2004

Proline-catalysed amination of alpha,alpha-disubstituted racemic aldehydes with azodicarboxylates proceeds smoothly to give configurationally stable scalemic aldehydes and oxazolidinones in up to 86% ee.

The conversion of diazonium tetrafluoroborate salts [1][2][3] into fluorinated arenes [4] was discovered more than 80 years ago by Balz and Schiemann, [5] and is widely used owing to the importance of fluorinated compounds in the life sciences [6] and material science [7] in academic as well as industrial laboratories. [8,9] This method has also found application for the synthesis of radioactive-labeled compounds.[10]The yields of the Balz-Schiemann reaction are moderate to good, and a few isolated protocols achieve excellent yields.[11] Therefore many attempts have been made to increase the yields and to lower the reaction temperatures, which in general correspond to the melting points of the tetrafluoroborates, in most cases over 100 8C. Some alternatives rely on, for example, the exchange of the counter ion [12] or the use of other solvents like BF 3 ·Et 2 O [13] and ionic liquids.[14] Modified conditions, for example photochemical methods, [15,16] have also resulted in improved protocols. Herein we describe a variant of the Balz-Schiemann reaction which through the utilization of a perfluorinated solvent leads to very good conversions of diazonium salts and triazenes to provide the corresponding aryl fluorides under mild conditions (Scheme 1). In our search for a method that allows the application of the Balz-Schiemann reaction in combinatorial chemistry, we tested different sets of conditions. Our leitmotiv was the cleavage of triazenes to give diazonium ions followed by their conversion in situ into the corresponding fluoroarenes. This approach, known as Wallach reaction, [17] offers some advantages over conventional methods. First, triazenes can be stored for extended periods without decomposition and they constitute safe alternatives to explosive diazonium salts. For example, our DSC/TG and DTA/TG measurements (DSC = dynamic difference calorimetry, DTA = differential thermoanalysis, TG = thermogravimetry) on triazene 9 (see Scheme 4) gave a decomposition temperature of 202.2 8C (beginning at 136 8C up to 266 8C, with a loss of mass of 98 %), while no reaction with O 2 or H 2 O takes place. The enthalpy of decomposition for 9 is determined to be roughly 40 kJ g À1 . In addition, triazene-masked diazonium ions can be used in reaction sequences in solution as well as on a solid support, and are thus amenable to combinatorial methods.[18] All products of the fluorinating cleavage should first be analyzed in terms of purity, as the isolation of preferably pure crude products plays a pivotal role in combinatorial chemistry.Initial tests were conducted with resin-bound triazenes. We used different solvents (for example, THF, DMF, MeOH) and observed the generation of "traceless" by-products (the reduced cleavage compound). As these compounds account for most of the impurities in the thermal decomposition of diazonium salts as well, we tried to suppress the reduction through the use of a perfluorinated solvent. In perfluorohexane [19] under optimized conditions, cleavage of the aromatic compounds to give the diazo...

Hexaazido and hexaiodo macrocyclic methanofullerenes undergo high-yielding sixfold click reactions or sixfold Heck, Sonogashira and Suzuki cross-coupling reactions, respectively, to yield all organic building blocks for higher molecular architectures.

A synthesis of an advanced intermediate towards the racemic form of the antiviral agent virantmycin has been developed featuring an intramolecular aza‐xylylene Diels–Alder reaction. The required arylthiocarbamate has been constructed using an efficient oxidative cyclization strategy. A novel synthetic approach to chlorine‐substituted allylic alcohols using an unprecedented palladium‐catalyzed cross‐coupling reaction of α,β‐unsaturated ketones and protected propargylic alcohols is reported.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)