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Friday, 14 March 2014
Tuesday, 11 March 2014
One-step synthesis of pyridines and dihydropyridines in a continuous flow microwave reactor
Figure 1: Microwave flow reactor for the Bohlmann–Rahtz synthesis of pyridine 2b.
read at
http://www.beilstein-journals.org/bjoc/single/articleFullText.htm?publicId=1860-5397-9-232
The Bohlmann–Rahtz pyridine synthesis and the Hantzsch dihydropyridine synthesis can be carried out in a microwave flow reactor or using a conductive heating flow platform for the continuous processing of material.
In the Bohlmann–Rahtz reaction, the use of a Brønsted acid catalyst allows Michael addition and cyclodehydration to be carried out in a single step without isolation of intermediates to give the corresponding trisubstituted pyridine as a single regioisomer in good yield.
Furthermore, 3-substituted propargyl aldehydes undergo Hantzsch dihydropyridine synthesis in preference to Bohlmann–Rahtz reaction in a very high yielding process that is readily transferred to continuous flow processing.
1Department of Chemistry, School of Life Sciences, University of Sussex, Falmer, Brighton, East Sussex, BN1 9QJ, UK
2School of Chemistry, Main Building, Cardiff University, Park Place, Cardiff, CF10 3AT, UK
3CEM Microwave Technology Ltd, 2 Middle Slade, Buckingham, MK18 1WA, UK
2School of Chemistry, Main Building, Cardiff University, Park Place, Cardiff, CF10 3AT, UK
3CEM Microwave Technology Ltd, 2 Middle Slade, Buckingham, MK18 1WA, UK
This article is part of the Thematic Series "Chemistry in flow systems III".
Guest Editor: A. Kirschning
Beilstein J. Org. Chem. 2013, 9, 1957–1968.
Peering Inside Reactors Analytical Chemistry: Microspectroscopy tracks multistep process in action
read all at
http://cen.acs.org/articles/92/i9/Peering-Inside-Reactors.html
It’s tough to get a detailed account of what’s going on inside catalytic chemical reactors while those workhorse pieces of equipment are running. If researchers could peer inside and monitor—at a microscopic level and in real time—the chemical reactions under way, they would gather a treasure trove of useful information. Engineers could then customize reactor geometry and dimensions and tailor the catalyst distribution to maximize energy efficiency, product output, and chemical selectivity.
That type of custom reactor engineering may be close at hand, thanks to a study conducted by researchers at the University of California, Berkeley, and Lawrence Berkeley National Laboratory.
The team designed a miniature reactor whose interior can be probed microscopically with infrared and X-ray beams. They used it to interrogate a multistep chemical reaction with extreme spatial resolution. The group pinpointed to within 15 μm the regions inside the reactor in which a flowing starting material was transformed to an initial product and then a final product. They correlated that information with the microscopic location, concentration, and chemical state of catalytic nanoparticles (J. Am. Chem. Soc. 2014, DOI: 10.1021/ja412740p).
Wednesday, 5 March 2014
Larvicidal isoxazoles: Synthesis and their effective susceptibility towards Aedes aegypti larvae
Larvicidal isoxazoles: Synthesis and their effective susceptibility towards Aedes aegypti larvae
Volume 21, Issue 4, 15 February 2013, Pages 940–947
Diana
C.B. da Silva-Alves, Janaína V. dos Anjos, Nery N.M. Cavalcante, Geanne
K.N. Santos, Daniela M.do A.F. Navarro, Rajendra M. SrivastavaTwenty 3,5-disubstituted isoxazoles have been synthesized and tested against fourth instar Aedes aegyptilarvae. In the synthesis of title compounds, modifications have been made in the C-5 side-chain with a view to test their larvicidal activity. These isoxazoles have been obtained by 1,3-dipolar cycloaddition of arylnitrile oxides to terminal alkynes which furnished the desired products in 20% to 79% yields. A comparative study of the larvicidal activity between 3-(3-aryl-isoxazol-5-yl)-propan-1-ols and 3-(3-aryl-isoxazol-5-yl)-propionic acids clearly demonstrated that the latter compounds possess much better larvicidal activity than the former. We also tested two esters, viz., methyl 3-[3-(phenyl)-isoxazole-5-yl] propionate and methyl 3-[3-(4-chlorophenyl)-isoxazole-5-yl] propionate, where the latter presented an excellent larvicidal profile.
Saturday, 1 March 2014
Thursday, 27 February 2014
Catalyst Under Stress
The oxidation of water to molecular oxygen is an important reaction in the frame of artificial photosynthesis, solar fuels, and a sustainable energy future. Iridium complexes have recently gained attention as effective precatalysts for this transformation.
To gain deeper understanding of this process, Alceo Macchioni, University of Perugia, Italy, and colleagues aimed at intercepting the intermediates of the oxidative transformation of [Cp*Ir(bzpy)NO3] (Cp* = pentamethylcyclopentadienyl, bzpy = 2-benzoylpyridine), which is a competent catalyst for water oxidation.
read at
http://www.chemistryviews.org/details/ezine/5838331/Catalyst_Under_Stress.html
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