Mechanistic studies on the CAN-mediated intramolecular cyclization of δ-aryl-β-dicarbonyl compounds

• Brian M. Casey,
• Dhandapani V. Sadasivam and
• Robert A. Flowers II

Beilstein J. Org. Chem. 2013, 9, 1472–1479, doi:10.3762/bjoc.9.167

• functionalized aromatic substrates undergo intramolecular cyclizations generating 2-tetralone derivatives in moderate to good yields. DFT computational studies indicate that successful formation of 2-tetralones from δ-aryl-β-dicarbonyl radicals is dependent on the stability of the subsequent cyclohexadienyl

• group was at the meta position (Table 2, entry 4). For substrates 1e and 1f with the methoxy group at either the ortho or para position, respectively, methyl esters 2e and 2f (Table 2, entries 2 and 3) were the major products. Additionally, intramolecular cyclizations with electron-deficient δ-aryl

• explain the site-selective radical cyclizations with m-methoxylated rings, the selectivity of naphthyl substrates was not investigated. The energy values for the cyclization of all substituents are given in Table 3, and their corresponding energy diagrams are given in Figure 1. For unsubstituted 1a’, the

Exploration of an epoxidation–ring-opening strategy for the synthesis of lyconadin A and discovery of an unexpected Payne rearrangement

• Brad M. Loertscher,
• Yu Zhang and
• Steven L. Castle

Beilstein J. Org. Chem. 2013, 9, 1179–1184, doi:10.3762/bjoc.9.132

• efficiently furnish its bicyclo[5.4.0]undecane system, which is shown in bold in Figure 1. Subsequent to this observation, we performed model studies that demonstrated the viability of highly stereoselective 7-exo-trig acyl radical–6-exo-trig alkyl radical cyclizations as a means of preparing bicyclo[5.4.0

Cascade radical reaction of substrates with a carbon–carbon triple bond as a radical acceptor

• Hideto Miyabe,
• Ryuta Asada and
• Yoshiji Takemoto

Beilstein J. Org. Chem. 2013, 9, 1148–1155, doi:10.3762/bjoc.9.128

• (Figure 1) [37][38][39][40][41][42][43]. Enantioselective radical reactions have been intensively studied over the past fifteen years. Compared with stereocontrol studies on intermolecular radical reactions, the enantioselective stereocontrol in radical cyclizations still remains a major challenge [44][45

• addition–cyclization–trapping reaction of substrates with a carbon–carbon triple bond as a radical acceptor as well as the scope and limitation of hydroxamate ester as a coordination site with a chiral Lewis acid. Synthetic strategies involving enantioselective radical cyclizations would be desirable tools

Tandem dinucleophilic cyclization of cyclohexane-1,3-diones with pyridinium salts

• Mostafa Kiamehr,
• Firouz Matloubi Moghaddam,
• Satenik Mkrtchyan,
• Volodymyr Semeniuchenko,
• Linda Supe,
• Alexander Villinger,
• Peter Langer and
• Viktor O. Iaroshenko

Beilstein J. Org. Chem. 2013, 9, 1119–1126, doi:10.3762/bjoc.9.124

• access to a number of bicyclic systems. Some of these reactions, such as the cyclization with quinazolinium salts, proceeded as one-pot cyclizations. Other cyclizations, such as the reaction with isoquinolinium salts, had to be carried out in two steps (formation of open-chained condensation products

• . Further studies to extend the scope of the synthetic utility of these cyclizations are in progress in both of our laboratories. Experimental General Information Solvents were purchased from ACROS and directly used without further purification. Analytical thin-layer chromatography was performed on 0.20 mm

Gold-catalyzed oxycyclization of allenic carbamates: expeditious synthesis of 1,3-oxazin-2-ones

• Benito Alcaide,
• Pedro Almendros,
• M. Teresa Quirós and
• Israel Fernández

Beilstein J. Org. Chem. 2013, 9, 818–826, doi:10.3762/bjoc.9.93

• ][37][38][39][40][41]. The Boc protective group has been widely used in allene chemistry, being an inert and recommended partner in gold- and palladium-catalyzed aminocyclizations of allenes [42]. On the other hand, reports of gold-catalyzed cyclizations leading to heterocycles that contain more than

Intramolecular carbolithiation cascades as a route to a highly strained carbocyclic framework: competition between 5-exo-trig ring closure and proton transfer

• William F. Bailey and
• Justin D. Fair

Beilstein J. Org. Chem. 2013, 9, 537–543, doi:10.3762/bjoc.9.59

• intramolecular 5-exo-trig ring closure has been well documented, and the absence of proton transfers that would compromise such cyclizations is a hallmark of this chemistry. In an effort to explore the limitations of this approach to more highly strained systems, the preparation of a stellane (tricyclo

• [3.3.0.03,7]octane) framework by an intramolecular carbolithiation cascade involving three coupled 5-exo-trig cyclizations of the vinyllithium derived from 2-bromo-4-vinyl-1,6-heptadiene by lithium–bromine exchange was investigated. The cascade does not afford the stellane; rather, the cascade is terminated

• after two cyclizations by a proton transfer that occurs by an intermolecular process catalyzed by trace amounts of endo-5-methyl-2-methylenebicyclo[2.2.1]heptane present in reaction mixtures as a consequence of inadvertent quenching of an intermediate alkyllithium during prolonged reaction times at room

Microwave-assisted three-component domino reaction: Synthesis of indolodiazepinotriazoles

• Rajesh K. Arigela,
• Sudhir K. Sharma,
• Brijesh Kumar and
• Bijoy Kundu

Beilstein J. Org. Chem. 2013, 9, 401–405, doi:10.3762/bjoc.9.41

• 1,3-dipolar cycloaddition reactions have been also applied by us and others with the view to synthesize triazole-annulated polyheterocycles. Although these cyclizations have been successfully carried out in either one-pot [22][23][24] or multistep format [25][26][27][28], reports involving their

Inter- and intramolecular enantioselective carbolithiation reactions

• Asier Gómez-SanJuan,
• Nuria Sotomayor and
• Esther Lete

Beilstein J. Org. Chem. 2013, 9, 313–322, doi:10.3762/bjoc.9.36

• , the aryllithium intermediate undergoes a tandem carbolithiation–γ-elimination leading to enantioenriched 2-cyclopropylphenols [51]. As shown, these enantioselective intramolecular cyclizations are mostly employed for the formation of five-membered rings. The 6-exo cyclization of an aryllithium

Polar reactions of acyclic conjugated bisallenes

• Reiner Stamm and
• Henning Hopf

Beilstein J. Org. Chem. 2013, 9, 36–48, doi:10.3762/bjoc.9.5

• converted into 54. Proton loss of this σ-complex yields the isolated aromatic product 57 in the last step. Thermal cyclizations of tetraenes such as 51 to aromatic compounds have been reported in the literature [31]. For the interception of the cations in Scheme 11 by bromide very similar results are

Intramolecular carbolithiation of N-allyl-ynamides: an efficient entry to 1,4-dihydropyridines and pyridines – application to a formal synthesis of sarizotan

• Wafa Gati,
• Mohamed M. Rammah,
• Mohamed B. Rammah and
• Gwilherm Evano

Beilstein J. Org. Chem. 2012, 8, 2214–2222, doi:10.3762/bjoc.8.250

• acidic and oxidative conditions would then afford the highly substituted dihydropyridine or pyridine derivatives 5 and 6, respectively. While there were no examples of such exclusive anionic 6-endo-dig cyclizations reported to the best of our knowledge [39], we felt that the presence of the chelating

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

• already oxidized by standing in air; the tetramethyl derivative 24 is stable towards air [139]. 1.4.3 Metal-induced reactions Although metal-initiated reactions (usually cyclizations) have become important ring-forming processes for the “higher” and heteroorganic bisallenes (see Sections 2.3 and 6.2

A quantitative approach to nucleophilic organocatalysis

• Herbert Mayr,
• Sami Lakhdar,
• Biplab Maji and
• Armin R. Ofial

Beilstein J. Org. Chem. 2012, 8, 1458–1478, doi:10.3762/bjoc.8.166

• Herbert Mayr Sami Lakhdar Biplab Maji Armin R. Ofial Department Chemie, Ludwig-Maximilians-Universität München, Butenandstr. 5-13 (Haus F), 81377 München, Germany 10.3762/bjoc.8.166 Abstract The key steps in most organocatalytic cyclizations are the reactions of electrophiles with nucleophiles

Parallel and four-step synthesis of natural-product-inspired scaffolds through modular assembly and divergent cyclization

• Hiroki Oguri,
• Haruki Mizoguchi,
• Hideaki Oikawa,
• Aki Ishiyama,
• Masato Iwatsuki,
• Kazuhiko Otoguro and
• Satoshi Ōmura

Beilstein J. Org. Chem. 2012, 8, 930–940, doi:10.3762/bjoc.8.105

• divergent cyclizations, we have developed a four-step synthetic process to yield a collection of natural-product-inspired scaffolds. Modular assembly of building blocks onto a piperidine-based manifold 6, having a carboxylic acid group, was achieved through Ugi condensation, N-acetoacetylation and

• subsequent installation of a diazoimide group. This allowed three-step access to collections of cyclization precursors with a linkage of the piperidine and the indole units as key substructures shared with naturally occurring alkaloids. Rhodium-catalyzed cyclizations of diazoimides and subsequent divergent

• composed of indole (red) and piperidine (blue) groups; (c) divergent cyclizations to generate scaffold variations as an illustration of the “Build-Couple-Pair” strategy in diversity-oriented synthesis. (a) Synthetic plans based on modular assembly and divergent cyclizations leading to fused skeletons; (b

An intramolecular inverse electron demand Diels–Alder approach to annulated α-carbolines

• Zhiyuan Ma,
• Feng Ni,
• Grace H. C. Woo,
• Sie-Mun Lo,
• Philip M. Roveto,
• Scott E. Schaus and
• John K. Snyder

Beilstein J. Org. Chem. 2012, 8, 829–840, doi:10.3762/bjoc.8.93

• annulations was previously noted by Taylor [95][96][97][98], and has been ascribed to the greater entropy loss for the larger rings [99]. Indeed, it has been estimated that the effective molarity for 5-membered ring closures can be as high as 1,000-fold greater in comparison to 6-membered ring cyclizations

N-Heterocyclic carbene/Brønsted acid cooperative catalysis as a powerful tool in organic synthesis

• Rob De Vreese and
• Matthias D’hooghe

Beilstein J. Org. Chem. 2012, 8, 398–402, doi:10.3762/bjoc.8.43

• -lactam to γ-lactam ring expansions [29][30], aziridine ring openings followed by cyclization with enolates [31], palladium-catalyzed cyclizations [32], cycloadditions [33], multicomponent reactions [34], and even NHC catalysis [35][36]. Nevertheless, the methodology developed by Rovis indisputably

Efficient, highly diastereoselective MS 4 Å-promoted one-pot, three-component synthesis of 2,6-disubstituted-4-tosyloxytetrahydropyrans via Prins cyclization

• Naseem Ahmed and
• Naveen Kumar Konduru

Beilstein J. Org. Chem. 2012, 8, 177–185, doi:10.3762/bjoc.8.19

• and unsymmetrical tetrahydropyrans can be synthesized. p-Toluenesulfonic acid (PTSA) is reported as a versatile Brønsted acid catalyst in various organic transformations [32][33][34]. Previously, PTSA has been used as a catalyst in Prins cyclizations but the product yields were low even under extended

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

• /MvdD) and one ω-amide linkage between lysine and aspartate (MdnB/MvdC) (Figure 10) [64][65]. Microviridins can be heterologously produced in E. coli [65]. Cyclizations occur in a strictly defined order. Ring size and composition of the microviridin core peptide is invariant [66], whereas N-terminal and

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

• demonstrated to be amongst the best catalysts in many gold(I)-catalyzed cyclizations [6][58]. No reaction was observed with complex 5 after heating for 5 min at 70 °C in CH2Cl2 under microwave irradiation (Table 1, entry 1), whereas the more electrophilic 6, bearing a less donating phosphite ligand, led almost

Access to pyrrolo-pyridines by gold-catalyzed hydroarylation of pyrroles tethered to terminal alkynes

• Elena Borsini,
• Gianluigi Broggini,
• Andrea Fasana,
• Chiara Baldassarri,
• Angelo M. Manzo and
• Alcide D. Perboni

Beilstein J. Org. Chem. 2011, 7, 1468–1474, doi:10.3762/bjoc.7.170

• on the C–C triple bond to direct the cyclization following 6-exo-dig or 7-endo-dig processes. Once again, the trend in terms of direct and rearranged product formation was dependent on the solvent, the 1,2-migration products being favoured in less polar solvents. The 7-endo-dig cyclizations of amides

PEG-embedded KBr₃: A recyclable catalyst for multicomponent coupling reaction for the efficient synthesis of functionalized piperidines

• Sanny Verma,
• Suman L. Jain and
• Bir Sain

Beilstein J. Org. Chem. 2011, 7, 1334–1341, doi:10.3762/bjoc.7.157

• –Alder reactions [22][23], intramolecular Michael reactions [24], intramolecular Mannich reactions onto iminium ions [25], tandem cyclopropane ring-opening/Conia-ene cyclizations [26], and aza-Prins-cyclization [27][28][29], have been reported for the synthesis of piperidines. However, these methods

Cyclization of 5-hexynoic acid to 3-alkoxy-2-cyclohexenones

• Anne T. Hylden,
• Eric J. Uzelac,
• Zeljko Ostojic,
• Ting-Ting Wu,
• Keely L. Sacry,
• Krista L. Sacry,
• Lin Xi and
• T. Nicholas Jones

Beilstein J. Org. Chem. 2011, 7, 1323–1326, doi:10.3762/bjoc.7.155

• ours is that our cyclizations are Lewis acid mediated. Building on the work of Tedder [7] and Smit [8][9] we have improved the alkynoic acid cyclization approach in a manner that allows ready access to 3-alkoxy-2-cyclohexenones in good yields. Further elaboration of this methodology is ongoing

Ugi post-condensation copper-triggered oxidative cascade towards pyrazoles

• Aurélie Dos Santos,
• Laurent El Kaim,
• Laurence Grimaud and
• Caroline Ronsseray

Beilstein J. Org. Chem. 2011, 7, 1310–1314, doi:10.3762/bjoc.7.153

• advantage of the functional group tolerance of the Ugi coupling to apply to these adducts the various cyclizations offered by the chemists toolkit. We became involved in the Ugi-post-condensation field through our initial interest in radical processes. We found that, compared with classical cycloadditions

Microphotochemistry: 4,4'-Dimethoxybenzophenone mediated photodecarboxylation reactions involving phthalimides

• Oksana Shvydkiv,
• Kieran Nolan and
• Michael Oelgemöller

Beilstein J. Org. Chem. 2011, 7, 1055–1063, doi:10.3762/bjoc.7.121

• cyclizations Two photodecarboxylative cyclization reactions were investigated with potassium phthaloyl-γ-aminobutyrate (3) and potassium phthalimidomethylsulfanylacetate (6) as starting materials [42]. A main advantage of these transformations is the ease of removal of the unreacted starting material by simple

Asymmetric Au-catalyzed cycloisomerization of 1,6-enynes: An entry to bicyclo[4.1.0]heptene

• Alexandre Pradal,
• Chung-Meng Chao,
• Patrick Y. Toullec and
• Véronique Michelet

Beilstein J. Org. Chem. 2011, 7, 1021–1029, doi:10.3762/bjoc.7.116

• % isolated yield respectively) resulting from 5-exo- and 6-endo cycloisomerization reactions [20][66]. Thus, the gold catalytic system cannot compete with the results obtained for the cyclizations of nitrogen-tethered enynes in the presence of iridium, platinum or rhodium catalysts [41][42][43][44][45]. The

Intramolecular hydroamination of alkynic sulfonamides catalyzed by a gold–triethynylphosphine complex: Construction of azepine frameworks by 7-exo-dig cyclization

• Hideto Ito,
• Tomoya Harada,
• Hirohisa Ohmiya and
• Masaya Sawamura

Beilstein J. Org. Chem. 2011, 7, 951–959, doi:10.3762/bjoc.7.106

• have geminal disubstitution or ring fusion within a linker chain connecting the attacking nitrogen atom and the alkyne moiety. It should be noted, however, that 7-“endo”-dig cyclizations of (o-alkynyl)phenylacetamides and a diynamide were achieved with gold and palladium complexes [39][46][52][53], and