Directed aromatic functionalization

• Victor Snieckus

Beilstein J. Org. Chem. 2011, 7, 1215–1218, doi:10.3762/bjoc.7.141

• causing a revolution in how we think about the preparation of aromatic/heteroaromatic molecules. Here, conceptually similar to the complex-induced proximity effect (CIPE) [31], which is operational in DoM reactivity, chelation of heteroatom groups to transition metals may be invoked, with an important

Homoallylic amines by reductive inter- and intramolecular coupling of allenes and nitriles

• Peter Wipf and
• Marija D. Manojlovic

Beilstein J. Org. Chem. 2011, 7, 824–830, doi:10.3762/bjoc.7.94

• dimethylzinc, both (E)- and (Z)-allylzinc species can exist in the solution. The chelation of the zirconocene to the ether oxygen and the imine nitrogen leads to a preference for the (Z)-TS species, paving the way for the formation of the observed cis-product. To further elaborate on the utility of this

Metathesis access to monocyclic iminocyclitol-based therapeutic agents

• Ileana Dragutan,
• Valerian Dragutan,
• Carmen Mitan,
• Hermanus C.M. Vosloo,
• Lionel Delaude and
• Albert Demonceau

Beilstein J. Org. Chem. 2011, 7, 699–716, doi:10.3762/bjoc.7.81

• atom economy. However, before carrying out the RCM reaction, the basic amino group (incompatible with most metathesis catalysts because of chelation to the metal center) [48] must either be protected (as N–Boc, N–Cbz, etc.), masked by incorporation into a cleavable heteroatom-containing cycle

A gold-catalyzed alkyne-diol cycloisomerization for the synthesis of oxygenated 5,5-spiroketals

• Sami F. Tlais and
• Gregory B. Dudley

Beilstein J. Org. Chem. 2011, 7, 570–577, doi:10.3762/bjoc.7.66

• the reported structure of cephalosporolide H (1) is outlined in Scheme 2. We recently demonstrated the use of inter-cycle chelation effects to control the spiroketal stereochemistry [28][29]. However, formation of the requisite oxygenated spiroketals (by cycloisomerization) posed significant

• single diastereomer upon chelation with zinc chloride. TEMPO oxidation gave lactone 1, which corresponds to the reported structure of cephalosporolide H. A more detailed discussion is found in our earlier report [28]. Two mechanistic alternatives (Scheme 7) are proposed for the conversion of 6 → 17 in

Stereoselective synthesis of four possible isomers of streptopyrrolidine

• Debendra K. Mohapatra,
• Barla Thirupathi,
• Pragna P. Das and
• Jhillu S. Yadav

Beilstein J. Org. Chem. 2011, 7, 34–39, doi:10.3762/bjoc.7.6

• determined by HPLC), which were easily separated by silica gel column chromatography. The stereochemical outcome in both the cases was explained by Crams’ rule, i.e., for a non-chelation model, the (R)-aldehyde would give rise to the (3S,4R) isomer. Alternatively, in a chelation model, the metal imposes a

The allylic chalcogen effect in olefin metathesis

• Yuya A. Lin and
• Benjamin G. Davis

Beilstein J. Org. Chem. 2010, 6, 1219–1228, doi:10.3762/bjoc.6.140

• sulfide could be explained with a sulfur relayed mechanism (Scheme 9a), where sulfur pre-coordination to the ruthenium center increases the effective concentration between the alkylidene and the alkene substrate. For the allyl sulfides this can occur without detrimental chelation, which is thought to be

Cross-metathesis of allylcarboranes with O-allylcyclodextrins

• Ivan Šnajdr,
• Zbyněk Janoušek,
• Jindřich Jindřich and
• Martin Kotora

Beilstein J. Org. Chem. 2010, 6, 1099–1105, doi:10.3762/bjoc.6.126

• reactions, which has also been observed in other metathetical reactions with alkenylcyclodextrins derivatives [27] and can be explained by several factors [28]. Firstly, by a chelation of the intermediate Ru-carbene complex to the oxygen atoms of the cyclodextrin which results in a conformationally rigid

Halide exchanged Hoveyda-type complexes in olefin metathesis

• Julia Wappel,
• César A. Urbina-Blanco,
• Mudassar Abbas,
• Jörg H. Albering,
• Robert Saf,
• Steven P. Nolan and
• Christian Slugovc

Beilstein J. Org. Chem. 2010, 6, 1091–1098, doi:10.3762/bjoc.6.125

• : leaving group, e.g. phosphine or pyridine; olive: carbine substituents; and dashed lines symbolise possibilities of chelation). Three commercial and frequently used catalysts (G2: Grubbs 2nd generation catalyst; M2: Neolyst M2; and 1: Hoveyda 2nd generation catalyst). Details of the 1H NMR spectra

Chromo- and fluorophoric water-soluble polymers and silica particles by nucleophilic substitution reaction of poly(vinyl amine)

• Katja Hofmann,
• Ingolf Kahle,
• Frank Simon and
• Stefan Spange

Beilstein J. Org. Chem. 2010, 6, No. 79, doi:10.3762/bjoc.6.79

• hydrolyzed PVFA contains ca. 5% of formamido groups and 95% of primary amino groups. The water-soluble PVAm copolymer has been widely applied for a number of purposes, e.g., in catalysis [7], chelation [8], treatment of waste water [9], paper making [10], recovery of oil [11] and as superabsorber [12

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

• species resulting from the addition of 1 equivalent of alkylmagnesium bromide [R1 = primary, secondary and benzyl groups] to 1 equivalent of copper salt leads, after reaction with electrophiles, to the unique formation of the linear adducts 11 in excellent isolated yields. The intramolecular chelation of

• (−40 instead of −78 °C), which can be attributed to a slow copper to magnesium contrathermodynamic transmetalation reaction, probably due to a strong intramolecular chelation of the sp2 organometallic derivative by the carbamate moiety. N-substituted alkynes Nitrogen-substituted alkynes (ynamine

• (branched/linear: 82/18), again showing that the chelation effect plays a major role in the regiochemistry of the carbometalation. The carbometalation of enantiomerically enriched cyclic ynamide 20 was recently used in a single-pot operation as a new entry to aldol products 21 possessing quaternary

Anion receptors containing thiazine-1,1-dioxide heterocycles as hydrogen bond donors

• Hong-Bo Wang,
• James A. Wisner and
• Michael C. Jennings

Beilstein J. Org. Chem. 2010, 6, No. 50, doi:10.3762/bjoc.6.50

• , occlude this central cleft like those of 1 and 2. Rather, they form a divergent “V”-shaped geometry upon chelation of anionic species by the two NH groups of 3, regardless of whether coplanarity is maintained with the central benzene ring. The ortho-protons of these terminal rings (Hc) are certainly too

Anthracene coupled adenine for the selective sensing of copper ions

• Kumaresh Ghosh and
• Tanushree Sen

Beilstein J. Org. Chem. 2010, 6, No. 44, doi:10.3762/bjoc.6.44

• presumably occur by the chelation enhanced anthracene → Cu2+ π-cation interactions, the paramagnetic effect of Cu2+ [34][35][36]. To understand the selective sensing of Cu2+ by both 1 and 2, we recorded the emission spectra of the receptors with the addition of 10 equivalents of Cu2+ to the receptor

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

An efficient partial synthesis of 4′-O-methylquercetin via regioselective protection and alkylation of quercetin

• Nian-Guang Li,
• Zhi-Hao Shi,
• Yu-Ping Tang,
• Jian-Ping Yang and
• Jin-Ao Duan

Beilstein J. Org. Chem. 2009, 5, No. 60, doi:10.3762/bjoc.5.60

• groups at position 3′ and 4′ in quercetin may be protected after chelation with borax [21]. However, the Wender group [22] and the Rolando group [23] reported that under these conditions quercetin methylation gave a complex mixture with at least three non-identified partially methylated quercetin ethers

The role of an aromatic group in remote chiral induction during conjugate addition of α-sulfonylallylic carbanions to ethyl crotonate

• Shlomo Levinger,
• Ranjeet Nair and
• Alfred Hassner

Beilstein J. Org. Chem. 2008, 4, No. 32, doi:10.3762/bjoc.4.32

• geometry of the aromatic ring during chelation with the lithiated species is as yet unknown, it evidently plays an important role in determining the approach of the carbanion to the conjugate acceptor and thus the stereoselectivity of the conjugate addition. Preliminary ab initio calculations [17] for the