Productive chloroarene C-cl bond activation: palladium/phosphine-catalyzed methods for oxidation of alcohols and hydrodechlorination of chloroarenes

The palladium/phosphine-catalyzed productive chloroarene C-Cl bond activation provides general, efficient, and functional group friendly methods for the selective oxidation of alcohols and the hydrodechlorination of chloroarenes.     

An organometallic inhibitor for glycogen synthase kinase 3

Replacing natural products with kinetically inert metal complexes may lead to a new class of therapeutics in which a metal center plays the role of an innocent bystander, organizing the orientation of the organic ligands in the receptor space. As an example of this approach, a ruthenium complex is described that copies the binding mode of indolocarbazole protein kinase inhibitors and serves as a reversible, low-nanomolar inhibitor for glycogen synthase kinase 3 (GSK-3).     

Highly regioselective synthesis of tetrahydro-2H-1,3-thiazin-2-ones via rhodium-catalyzed carbonylation of N-alkylisothiazolidines

[reaction: see text] The [Rh(COD)Cl]2- and KI-catalyzed carbonylation of functionalized N-alkylisothiazolidines in toluene gives the corresponding tetrahydro-2H-1,3-thiazin-2-ones in good yield. The carbonylation reaction occurred site-selectively at the S-N bond of the isothiazolidine ring. The reaction is believed to proceed via oxidative addition, followed by CO insertion and reductive elimination to form the tetrahydro-2H-1,3-thiazin-2-one derivatives.     

Low temperature single crystal X-ray diffraction: advantages, instrumentation and applications

The benefits of carrying out single crystal X-ray diffraction (SXRD) experiments at low temperatures have long been recognised by the scientific community, as clearly demonstrated by the massive increase in publications reporting the use of low temperature SXRD in the past 15 years. This tutorial review will summarise the advantages, many of them now often forgotten by its practitioners or never known by the newcomers to the field, of performing single crystal X-ray diffraction experiments at low temperatures. The instrumentation currently available to university laboratories, which has been greatly improved over the past 5 years, will also be briefly described and a few different examples covering a range of applications will be presented.     

Spectrofluorimetric determination of surface-bound thiol groups and its application to the analysis of thiol-modified silicas

A sensitive spectofluorimetric method has been developed for the quantitative measurement of surface-bound thiol groups. The procedure is based on the quantitative esterification of the thiol group with Rhodamine B and its subsequent release from the solid by base hydrolysis for spectrofluorimetric determination. Application of the method to the analysis of thiol-modified nanoparticulate silicas yielded results that compared favourably against alternative approaches based on measurements of mercury capacity and iodometric titration of the thiol groups. Non-specific Rhodamine uptake, assessed using unmodified silica and C18-modified silica, did not significantly influence the analytical results. When applied to a typical 50 mg sample, the detection limit of the procedure was 1 nmole SH g(-1) silica.     

Synthesis of a novel C2-aryl substituted 1,2-unsaturated pyrrolobenzodiazepine

A novel C2-aryl 1,2-unsaturated PBD (14) has been prepared via an enol triflate intermediate (8). The regiochemistry of triflation is dependent upon the point at which the reaction is performed during the synthetic route.     

Dioxygenase-catalysed oxidation of monosubstituted thiophenes: sulfoxidation versus dihydrodiol formation

Toluene dioxygenase (TDO)-catalysed sulfoxidation, using Pseudomonas putida UV4, was observed for the thiophene substrates 1A-1N. The unstable thiophene oxide metabolites, 6A-6G, 6K-6N, spontaneously dimerised yielding the corresponding racemic disulfoxide cycloadducts 7A-7G, 7K-7N. Dimeric or crossed [4 + 2] cycloaddition products, derived from the thiophene oxide intermediates 6A and 6D or 6B and 6D, were found when mixtures of thiophene substrates 1A and 1D or 1B and 1D were biotransformed. The thiophene sulfoxide metabolite 6B was also trapped as cycloadducts 17 or 18 using stable dienophiles. Preferential dioxygenase-catalysed oxidation of the substituent on the thiophene ring, including exocyclic sulfoxidation (1H-1J) and cis-dihydroxylation of a phenyl substituent (1G and 1N), was also observed. An enzyme-catalysed deoxygenation of a sulfoxide in P. putida UV4 was noticed when racemic disulfoxide cyclo-adducts 7A, 7B and 7K were converted to the corresponding enantioenriched monosulfoxides 8A, 8B and 8K via a kinetic resolution process. The parent thiophene 1A and the 3-substituted thiophenes 1K-1N were also found to undergo ring dihydroxylation yielding the cis/trans-dihydrodiol metabolites 9A and 9K-9N. Evidence is provided for a dehydrogenase-catalysed desaturation of a heterocyclic dihydrodiol (9Kcis/9Ktrans) to yield the corresponding 2,3-dihydroxythiophene (24) as its preferred thiolactone tautomer (23). A simple model to allow prediction of the structure of metabolites, formed from TDO-catalysed bacterial oxidation of thiophene substrates 1, is presented.     

Productive utilization of chlorobenzene: palladium-catalyzed selective oxidation of alcohols

[reaction: see text] The palladium/ligand-catalyzed activation of chlorobenzene provides a general, efficient, and functional group friendly method for the selective oxidation of alcohols to carbonyl compounds.     

Spirocyclopropanated bicyclopropylidenes: straightforward preparation, physical properites, and chemical transformations

Perspirocyclopropanated bicyclopropylidene (6) was prepared in three steps from 7-cyclopropylidenedispiro[2.0.2.1]heptane (4) (24% overall) or, more efficiently, through dehalogenative coupling of 7,7-dibromo[3]triangulane (15) (82%). This type of reductive dimerization turned out to be successful for the synthesis of (E)- and (Z)-bis(spiropentylidene) 14 (67%) and even of the "third-generation" spirocyclopropanated bicyclopropylidene 17 (17% overall from 15). Whereas the parent bicyclopropylidene 1 dimerized at 180 degrees C to yield [4]rotane, dimerization of 6 at 130 degrees C under 10 kbar pressure occured only with opening of one three-membered ring to yield the polyspirocyclopropanated (cyclopropylidene)cyclopentane derivative 19 (34% yield), and at the elevated temperature the polyspirocyclopropanated 2-cyclopropylidene[3.2.2]propellane derivative 20 (25 % yield). Perspirocyclopropanated bicyclopropylidene 6 and the "third-generation" bicyclopropylidene 17 gave addition of bromine, hydrogen bromide, and various dihalocarbenes without rearrangement. The functionally substituted branched [7]triangulane 28 and branched dichloro-C2v-[15]triangulane 32 were used to prepare the perspirocyclopropanated [3]rotane (D3h-[10]triangulane) 49 (six steps from 6, 1.4% overall yield) and the C2v-[15]triangulane 51 (two steps from 17, 41% overall). Upon catalytic hydrogenation, the perspirocyclopropanated bicyclopropylidene 6 yielded 7,7'-bis(dispiro[2.0.2.]-heptyl) (52) and, under more forcing conditions, 1,1'-bis(2,2,3,3-tetramethylcyclopropyl) (53). The bromofluorocarbene adduct 33 of 17 reacted with butyllithium to give the unexpected polyspirocyclopropanated 1,4-di-n-butyl-2-cyclopropylidenebicyclo[2.2.0]hexane derivative 37 as the main product (55% yield) along with the expected "third-generation" perspirocyclopropanated dicyclopropylidenemethane 38 (21% yield). Mechanistic aspects of this and the other unusual reactions are discussed. The structures of all new unusual hydrocarbons were proven by X-ray crystal structure analyses, and the most interesting structural and crystal packing features are presented.