Natural product biosyntheses in cyanobacteria: A treasure trove of unique enzymes

• Jan-Christoph Kehr,
• Douglas Gatte Picchi and
• Elke Dittmann

Beilstein J. Org. Chem. 2011, 7, 1622–1635, doi:10.3762/bjoc.7.191

• shown to introduce β-branching carboxyl units into a number of polyketide chains. Feeding studies for jamaicamides revealed the incorporation of an acetate unit at the corresponding position followed by dehydratisation, decarboxylation and halogenation [41]. Further interesting features of jamaicamide

• halogenation domain, although this could not be expected from the structure of curacin A. In vitro studies revealed that indeed cyclopropyl ring formation is preceded by a halogenation step (Figure 6B) [42]. The Cur ECH2 was found to catalyze the formation of a α,β-enoyl thioester, which is in contrast to the

Recent advances in direct C–H arylation: Methodology, selectivity and mechanism in oxazole series

• Cécile Verrier,
• Pierrik Lassalas,
• Laure Théveau,
• Guy Quéguiner,
• François Trécourt,
• Francis Marsais and
• Christophe Hoarau

Beilstein J. Org. Chem. 2011, 7, 1584–1601, doi:10.3762/bjoc.7.187

• regioselective functionalization. Ortho-lithiation by means of alkyllithium and lithium amides bases has been extensively developed as lithiated species display a high reactivity towards many electrophiles, leading to various substitutions (e.g., halogenation, carboxylation, acylation, hydroxymethylation

Development of the titanium–TADDOLate-catalyzed asymmetric fluorination of β-ketoesters

• Lukas Hintermann,
• Mauro Perseghini and
• Antonio Togni

Beilstein J. Org. Chem. 2011, 7, 1421–1435, doi:10.3762/bjoc.7.166

• substrate range of the catalytic fluorination and its extension to other activated carbonyl compounds [57]. Results and Discussion Lewis acid catalyzed halogenation of activated carbonyl compounds Overview Nonfunctionalized ketones are halogenated in the α-position by halogens and other electrophilic

• equilibirum mixture is halogenated quickly, leaving behind the keto tautomer [63]. Further halogenation is then limited by the rate of enolization. This effect forms the basis of Meyer’s famous enol-titration experiments for determining the degree of enolization in activated carbonyl compounds (Scheme 2a) [63

• should also result in catalysis of the overall electrophilic halogenation. As a working hypothesis, it was assumed that coordination of β-ketocarbonyl compounds to Lewis acidic metal centers should facilitate their transformation to a covalently coordinated enolate, which may be fluorinated at carbon

One-pot four-component synthesis of pyrimidyl and pyrazolyl substituted azulenes by glyoxylation–decarbonylative alkynylation–cyclocondensation sequences

• Charlotte F. Gers,
• Julia Rosellen,
• Eugen Merkul and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2011, 7, 1173–1181, doi:10.3762/bjoc.7.136

• , azulenes must be functionalized, either by halogenation or borylation, and some of these derivatives were found to be quite unstable [45][46]. To the best of our knowledge, no diversity-oriented multicomponent syntheses of azulenyl heterocycles have been reported so far. Here, we report the development of

Aromatic and heterocyclic perfluoroalkyl sulfides. Methods of preparation

• Vladimir N. Boiko

Beilstein J. Org. Chem. 2010, 6, 880–921, doi:10.3762/bjoc.6.88

• . The halogenation of SAlk-derivatives with subsequent replacement of the halogen atoms by fluorine. The introduction of SRF-moieties into aromatic compounds by both electrophilic and nucleophilic reagents. Various modes of perfluoroalkylation of organosulfur compounds including cationic, anionic

• groups. The reactions are more problematic however, for electron deficient substrates where competing halogenation, reduction and isomerization products often result from perfluoroalkylthiolation reactions. 3.2. Nucleophilic introduction of SRF groups Anionic salts of type RFS− M+ and their heavy metal

Recent advances in carbocupration of α-heterosubstituted alkynes

• Ahmad Basheer and
• Ilan Marek

Beilstein J. Org. Chem. 2010, 6, No. 77, doi:10.3762/bjoc.6.77

• adducts (Scheme 22). Hydrolysis, alkylation, acylation, halogenation and stannylation proceed stereoselectively to afford synthetically useful intermediates [56][57]. Under similar conditions, 1-substituted alkynylsilanes do not undergo the carbometalation reaction. Only when 1-substituted-2

Palladium- catalyzed cross coupling reactions of 4-bromo- 6H-1,2-oxazines

• Reinhold Zimmer,
• Elmar Schmidt,
• Michal Andrä,
• Marcel-Antoine Duhs,
• Igor Linder and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2009, 5, No. 44, doi:10.3762/bjoc.5.44

• -hexyne provided alkynyl-substituted pyridine derivative 12 thus demonstrating the potential of this approach for the synthesis of pyridines. Keywords: alkyne; halogenation; 1,2-oxazines; palladium catalysis; pyridines; Introduction A broad range of synthetic applications demonstrates that 1,2-oxazine

• , we describe our results dealing with the halogenation of 6H-1,2-oxazines 1 and the use of the resulting products as precursors in palladium-catalyzed cross coupling reactions. Results and Discussion Not much is known about halogenated 6H-1,2-oxazines and only a few mostly inefficient procedures are

The use of silicon- based tethers for the Pauson- Khand reaction

• Adrian P. Dobbs,
• Ian J. Miller and
• Saša Martinović

Beilstein J. Org. Chem. 2007, 3, No. 21, doi:10.1186/1860-5397-3-21

• order to achieve this it was thought to form each of the 'arms' of the acetal in separate synthetic steps (Scheme 15). The first stage of the reaction was silyl ether formation. The alkyne 'arm' of the acetal was introduced first, as it was feared that during the next, halogenation step, halogenation of