Organocatalytic C–H activation reactions

• Subhas Chandra Pan

Beilstein J. Org. Chem. 2012, 8, 1374–1384, doi:10.3762/bjoc.8.159

• explanation is the formation of azomethine ylide intermediate 11 (Scheme 8) [19][20]. The carbanion of ylide 11 is then protonated by benzoic acid, and the resulting benzoate anion supports the aromatization process. In fact, Seidel and co-workers provided the experimental evidence for the existence of

• acid to form intermediate A. Azomethine ylide 13 is then produced by extrusion of acetic acid from intermediate A. Protonation of 13 generates another O-acetyl intermediate B, and finally, regeneration of acetic acid and aromatization provides the pyrrole product 7q. Pan and Seidel also independently

Highly selective synthesis of (E)-alkenyl-(pentafluorosulfanyl)benzenes through Horner–Wadsworth–Emmons reaction

• George Iakobson and
• Petr Beier

Beilstein J. Org. Chem. 2012, 8, 1185–1190, doi:10.3762/bjoc.8.131

• (product not isolated). Compound 10d was fully characterized by spectroscopic methods, and the yield was increased to 51% by performing the diazotization reaction in the absence of a reducing reagent (Scheme 3). Aromatization of 10d by oxidation using CAN was performed to give SF5-substituted phenanthrene

Discovery of practical production processes for arylsulfur pentafluorides and their higher homologues, bis- and tris(sulfur pentafluorides): Beginning of a new era of “super-trifluoromethyl” arene chemistry and its industry

• Teruo Umemoto,
• Lloyd M. Garrick and
• Norimichi Saito

Beilstein J. Org. Chem. 2012, 8, 461–471, doi:10.3762/bjoc.8.53

• gaseous SF5Cl with acetylene, followed by bromination, dehydrobromination, and reduction with zinc, giving pentafluorosulfanylacetylene (HC≡CSF5), which was then reacted with butadiene, followed by an aromatization reaction at very high temperature, gave phenylsulfur pentafluoride [35]. Recently

• , phenylsulfur pentafluoride was prepared by reaction of 1,4-bis(acetoxy)-2-cyclohexene with SF5Br under 250 W sunlamp irradiation, followed by dehydrobromination and then aromatization reactions [36]. A triethylborane-catalyzed reaction of 4,5-dichloro-1-cyclohexene with SF5Cl followed by dehydrochlorination

Syntheses and applications of furanyl-functionalised 2,2’:6’,2’’-terpyridines

• Jérôme Husson and
• Michael Knorr

Beilstein J. Org. Chem. 2012, 8, 379–389, doi:10.3762/bjoc.8.41

• dihydropyridine 32. The latter undergoes aromatization upon reaction with benzoquinone to afford 33 (Scheme 6). Synthesis by cross-coupling reaction Cross-coupling reactions are widely used in organic chemistry [32] to create new C–C bonds. The importance of this technique was recently highlighted by the award of

Photochemical and thermal intramolecular 1,3-dipolar cycloaddition reactions of new o-stilbene-methylene-3-sydnones and their synthesis

• Kristina Butković,
• Željko Marinić,
• Krešimir Molčanov,
• Biserka Kojić-Prodić and
• Marija Šindler-Kulyk

Beilstein J. Org. Chem. 2011, 7, 1663–1670, doi:10.3762/bjoc.7.196

• (Scheme 4) in which, as expected for the predicted structures, the aromatization reaction took place forming the pyrazolo-isoindole 13. Compound 13 arose also on silica gel during the purification of either 11 or 12. The irradiation of 3a or 3b until full conversion, as previously mentioned, produced a

• pathway of sydnone ring (N–CH) and trans- and cis-stilbene (α–β). Thermal and photochemical intermolecular [3 + 2] cycloadditions. Synthesis of the target molecules 3a and 3b. Photolysis of cis- or trans-3. Aromatization with DDQ. Possible mechanism for the formation of the photoproducts. Thermal reaction

Synthesis of fluoranthenes by hydroarylation of alkynes catalyzed by gold(I) or gallium trichloride

• Sergio Pascual,
• Christophe Bour,
• Paula de Mendoza and
• Antonio M. Echavarren

Beilstein J. Org. Chem. 2011, 7, 1520–1525, doi:10.3762/bjoc.7.178

• triaryl substituted diacenaphtho[1,2-j:1',2'-l]fluoranthenes (decacyclenes) 2a and 2b in very good overall yields after aromatization of the crude products with DDQ. Remarkably, this triple hydroarylation occurs efficiently with an average yield per C–C bond formation that is greater than 90%. Conclusion

Recent developments in gold-catalyzed cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2011, 7, 1075–1094, doi:10.3762/bjoc.7.124

• authors proposed an initial nucleophilic attack of the carbonyl oxygen on the gold(I)-activated alkyne to form a vinyl–gold intermediate XII, analogous to that previously shown in Scheme 5 (IX). Aromatization of this intermediate through C–C bond cleavage of the oxirane unit, followed by addition of the

Functionalization of anthracene: A selective route to brominated 1,4-anthraquinones

• Kiymet Berkil Akar,
• Osman Cakmak,
• Orhan Büyükgüngör and
• Ertan Sahin

Beilstein J. Org. Chem. 2011, 7, 1036–1045, doi:10.3762/bjoc.7.118

• of hexabromotetrahydroanthracene 6. Base-promoted aromatization of 7 and 8 afforded synthetically valuable tribromo-1-methoxyanthracenes 10 and 11. The reaction of 17 with sodium methoxide generated tribromodihydroanthracene-1,4-diol 27, whose oxidation with PCC gave 2,9,10-tribromoanthracene-1,4

• derivatives that are difficult to prepare by other routes. The studies also reveal the broad range of reactivity and selectivity of the stereoisomeric anthracene derivatives. Keywords: anthracene derivatives; anthracene-1,4-dione; aromatization; bromination; bromoanthracene; methoxyanthracene; silver-induced

• hexabromides 2 and 3 (Scheme 1) [1]. These studies revealed that hexabromides 2 and 3 are good precursors for the preparation of anthracene oxides and methoxyanthracene derivatives by silver ion-induced substitution. Our previous studies revealed that aromatization of hexabromides 2 and 3 showed complete

Recent advances in the gold-catalyzed additions to C–C multiple bonds

• He Huang,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

• indole. Further intramolecular nucleophilic attack of the phenyl group on the carbene carbon center, followed by a re-aromatization step and subsequent protodemetalation, affords 248 as the final product. Treatment of N-tethered 2,3-butadienyl-1H-indole 249 with di-tert-butyl(o-biphenyl)phosphine and

Gold(I)-catalyzed formation of furans by a Claisen-type rearrangement of ynenyl allyl ethers

• Florin M. Istrate and
• Fabien Gagosz

Beilstein J. Org. Chem. 2011, 7, 878–885, doi:10.3762/bjoc.7.100

• furnish the intermediate 9. The loss of a proton to allow aromatization of the system, followed by a protodemetalation step would finally give furan 7. In summary, we have developed a new gold(I)-catalyzed formation of polysubstituted furans, which is characterized by its efficiency, the mild conditions

When gold can do what iodine cannot do: A critical comparison

• Sara Hummel and
• Stefan F. Kirsch

Beilstein J. Org. Chem. 2011, 7, 847–859, doi:10.3762/bjoc.7.97

• alkaloid cleistopholine (41) from the aminoquinone 40 was easily achieved after in-situ aromatization of the intermediate to yield the desired compound in 60% yield. Furthermore, Wang and co-workers investigated a totally analogous cycloisomerization sequence using iodine as the electrophile to activate

Synthesis of novel 5-alkyl/aryl/heteroaryl substituted diethyl 3,4-dihydro-2H-pyrrole-4,4-dicarboxylates by aziridine ring expansion of 2-[(aziridin-1-yl)-1-alkyl/aryl/heteroaryl-methylene]malonic acid diethyl esters

• Satish S. More,
• T. Krishna Mohan,
• Y. Sateesh Kumar,
• U. K. Syam Kumar and
• Navin B. Patel

Beilstein J. Org. Chem. 2011, 7, 831–838, doi:10.3762/bjoc.7.95

• ; ii) POCl3, n-Bu3N, reflux; iii) THF, rt; iv) NaI, acetone, rt, overnight. Hydrolytic decarboxylation. Reagents and conditions: i) DMSO, LiCl catalytic water, 140–150 °C, 3 h; ii) DMSO, LiCl, catalytic water, 100–110 °C, 12 h. Reduction and aromatization of 2-substituted pyrrolines. Reaction

Synthetic applications of gold-catalyzed ring expansions

• David Garayalde and
• Cristina Nevado

Beilstein J. Org. Chem. 2011, 7, 767–780, doi:10.3762/bjoc.7.87

• in the substrate or adventitious water or alcohol present in the reaction media) opening of the three membered ring, followed by metal activation of the triple bond to trigger the cyclization (Scheme 9, lower row). In both cases, aromatization and protodeauration would afford the observed products

Novel carbazole–pyridine copolymers by an economical method: synthesis, spectroscopic and thermochemical studies

• Aamer Saeed,
• Madiha Irfan and
• Shahid Ameen Samra

Beilstein J. Org. Chem. 2011, 7, 638–647, doi:10.3762/bjoc.7.75

• cyclization and aromatization. The polymers were obtained by pouring the reaction mixture into distilled water, followed by filtration and washing of the residue with copious quantities of distilled water to remove completely acetic acid and salts. Finally, the polymers were dissolved in THF and re

The arene–alkene photocycloaddition

• Ursula Streit and
• Christian G. Bochet

Beilstein J. Org. Chem. 2011, 7, 525–542, doi:10.3762/bjoc.7.61

• completely new reaction Sakamoto has proposed a mechanism involving a ζ-hydrogen abstraction to form a biradical intermediate (Scheme 35, E). The resulting biradical cyclizes to form the spiro compound F upon recombination of the biradical. Re-aromatization affords the carboxylate G, which further attacks

• can take place to form a spiro compound; further re-aromatization to form the enol, lactolization and cyclization explains the formation of the benzoxepine structure [101]. Griesbeck et al. reported the formation of benzoxepines from the benzophenone analogue upon irradiation at slightly lower

• UV absorption band at 380 nm was observed. This absorption band fits well with TD-DFT calculations. He proposes that re-aromatization of this intermediate takes place via a zwitterionic species or through a proton catalyzed pathway. We recently found in our laboratories that the intramolecular

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

• (Scheme 23). First, the phenol acetate was replaced by a benzyl group. Among the different oxidants screened for dihydroxylation, osmium tetroxide was preferred, since it did not effect aromatization of the indoline ring and gave diol 83 as a single isomer. Dihydroxylation occurred selectively from the

An expedient synthesis of 5-n-alkylresorcinols and novel 5-n-alkylresorcinol haptens

• Kirsti Parikka and
• Kristiina Wähälä

Beilstein J. Org. Chem. 2009, 5, No. 22, doi:10.3762/bjoc.5.22

• -dimethoxybenzaldehyde (18–48% yields whenever reported) [22][23][24][25][26]. Additional synthetic methods have been developed for shorter chain AR (aromatization of cyclohexane derivatives in 61–66% yield [27]. A recent Wittig approach utilises the ozonolysis product of a pentadecylresorcinol (C15

Highly brominated anthracenes as precursors for the convenient synthesis of 2,9,10-trisubstituted anthracene derivatives

• Osman Cakmak,
• Leyla Aydogan,
• Kiymet Berkil,
• Ilhami Gulcin and
• Orhan Buyukgungor

Beilstein J. Org. Chem. 2008, 4, No. 50, doi:10.3762/bjoc.4.50

• effective and convenient method to prepare hexabromide 3. Most of the product precipitated during the reaction. After the reaction, a rapid and simple recrystallization gave the pure hexabromide 3 in 95% yield. As hexabromide 4 is quite sensitive to daylight and temperature, aromatization and epimerization

• ). Hexabromide 3 was subjected to aromatization with various bases. Treatment of hexabromide 3 with sodium methoxide or DBU led to a mixture of tetrabromide 11 [24], tribromide 12, and dibromide 2, while NaOH produced dibromide 2 (Scheme 3). Lastly, the reaction with pyridine efficiently and selectively afforded

• demonstrated that the bromination conditions of 9,10-dibromoanthracene dramatically affect the nature of the stereoisomeric hexabromide product and ratio. The studies also revealed that aromatization of hexabromide 3 depends strongly on the choice of base. Experimental General Thin layer chromatography was

Desymmetrization of 7-azabicycloalkenes by tandem olefin metathesis for the preparation of natural product scaffolds

• Wolfgang Maison,
• Marina Büchert and
• Nina Deppermann

Beilstein J. Org. Chem. 2007, 3, No. 48, doi:10.1186/1860-5397-3-48

• aromatization to 9 was the reason for the low catalytic efficiency of this conversion and tested this hypothesis with the conversion of the corresponding pentenoyl derivative 10 under RORCM conditions. As outline in Scheme 2, this reaction gave the expected metathesis product, which was hydrogenated to the

• isoindole derivative 11 in good yield, verifying our previous assumptions. As a general trend, it turned out that benzannelated azabicycloalkene derivatives like 8 and 10 give relatively unstable products. In consequence, products can only be isolated as pyridones 9, derived from spontaneous aromatization

Variations in product in reactions of naphthoquinone with primary amines

• Marjit W. Singh,
• Anirban Karmakar,
• Nilotpal Barooah and
• Jubaraj B. Baruah

Beilstein J. Org. Chem. 2007, 3, No. 10, doi:10.1186/1860-5397-3-10

• based on the established fact that the presence of a carbonyl group favors γ-attack on a α-β unsaturated carbonyl over an imine; we would like to put forward the first path. But it is still not clear about the aromatization process, whether it is a unimolecular, or a bimolecular process. Work is in