Locking of the longitudinal modes of an SBS-laser oscillator by optical feedback

The use of a nonlinear mirror on the basis of the stimulated Brillouin scattering (SBS) as part of a resonator in a laser oscillator leads to the generation of bandwidth due to the shift in frequency that is connected with the reflection at the SBS-mirror. Another effect of the nonlinear SBS-reflection is a passive Q-switch, which leads to a generation of pulses with durations of approximately 100 ns. An almost perfect locking of the longitudinal modes is observed if an additional external resonator is applied and certain resonance criteria are obeyed. This locking of the longitudinal modes surfaces as a splitting of the Q-switch pulses into trains of pulses with subnanosecond duration. PACS 42.60.Fc; 42.60.Gd; 42.65.Es     

Synthesis of 3‐Acetyl‐4‐hydroxy‐1‐phenylpyridin‐2(1H)‐one Derivatives

The cyclization of aryl ketone anilides 3 with diethyl malonate to affords 4‐hydroxy‐6‐phenyl‐6H‐pyrano[3,2‐c]‐pyridin‐2,5‐diones 4 in good yields. 3‐Acetyl‐4‐hydroxy‐1‐phenylpyridin‐2(1H)‐ones 5 are obtained by ring‐opening reaction of 4‐hydroxy‐6‐phenyl‐6H‐pyrano[3,2‐c]‐pyridin‐2,5‐diones 4 in the presence of 1,2‐diethylene glycol. The reaction of 3‐acetyl‐4‐hydroxy‐1‐phenylpyridin‐2(1H)‐ones 5 with hydroxylamine hydrochloride produces 4‐hydroxy‐3‐[N‐hydroxyethanimidoyl]‐1‐phenylpyridin‐2(1H)‐ones 6 from which 3‐alkyloxyiminoacetyl‐4‐hydroxy‐1‐phenylpyridin‐2(1H)‐ones 7 are obtained by reacting with alkyl bromides or iodides in the presence of anhydrous potassium carbonate with moderate yields. The similar compounds can be synthesized on refluxing 3‐acetyl‐4‐hydroxy‐1‐phenylpyridin‐2(1H)‐ones 5 with substituted hydroxylamine hydrochloride in the presence of sodium bicarbonate with good yields. Most of the synthesized compounds are characterized by IR and NMR spectroscopic methods.     

Microwave-assisted solution- and solid-phase synthesis of 2-amino-4-arylpyrimidine derivatives

An efficient and rapid microwave-assisted solution-phase method for the synthesis of 2-amino-4-arylpyrimidine-5-carboxylic acid derivatives has been developed. The five-step linear protocol involves an initial Biginelli multicomponent reaction leading to dihydropyrimidine-2-thiones which are subsequently S-alkylated with methyl iodide. The resulting 2-methylthiodihydropyrimidines are sequentially oxidized first with manganese dioxide and then with Oxone to provide 2-methylsulfonyl-pyrimidines which serve as excellent precursors for the generation of a variety of 2-substituted pyrimidines via displacement of the reactive sulfonyl group with nitrogen, oxygen, sulfur, and carbon nucleophiles. A modified protocol using a solid-phase method has also been developed.     

Synthesis of novel pyrano fused quinolones,coumarins, and pyridones

Dedicated to Professor Dr. Hans Junek, Graz, on the occasion of his 70th birthday A novel efficient synthesis of pyrano fused heterocycles namely, pyrano[3,2-c]quinoline-2,5(6H)-diones 3a-e, 7b-d , pyrano[3,2-c]benzopyran-2,5(6H)-dione ( 7f ), and pyrano[3,2-c]pyridine-2,5(6H)-diones 10, 11 was achieved by the condensation of 4-hydroxy-2-(1H)-quinolones 1a-e , 4-hydroxycoumarin ( 1f ), or 4-hydroxy-2(1H)-pyridone ( 9 ) with α-acetyl-γ-butyrolactone ( 2 ) or the sodium salt of α-formyl-γ-butyrol-actone ( 6 ), respectively, in the presence of ammonium acetate.     

Continuous Flow Organic Synthesis under High‐Temperature/Pressure Conditions

Microreactor technology and continuous flow processing in general are key features in making organic synthesis both more economical and environmentally friendly. When preformed under a high‐temperature/pressure process intensification regime many transformations originally not considered suitable for flow synthesis owing to long reaction times can be converted into high‐speed flow chemistry protocols that can operate at production‐scale quantities. This Focus Review summarizes the state of the art in high‐temperature/pressure microreactor technology and provides a survey of successful applications of this technique from the recent synthetic organic chemistry literature.     

Synthesis of poly(ε-caprolactone) diols and EO-CL block copolymers and their characterization by liquid chromatography and MALDI-TOF-MS

Polymers of ε-caprolactone were synthesized by microwave-assisted polymerization initiated with polyethylene glycols (PEG 200 and PEG 300) and monodisperse diols (mono-, di-, tri-, tetra- and hexaethylene glycol) and tin octoate as catalyst. These polymers were characterized by different chromatographic techniques (SEC, LAC and LCCC) and MALDI-TOF-MS. A comparison with commercially available polycaprolactone diols with molecular weight 530 and 830 showed that the new polymers had a much higher content of triblock structures, while the commercial samples contained considerable amounts of diblocks.