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

• reactions [41][42]. As a logical extension, one might speculate about analogous processes triggered by direct iodonium activation in the absence of gold catalysts (Scheme 1c). Since Barluenga, Larock, and others have shown over the last decades that various cyclizations of carbon and heteroatom nucleophiles

• stabilizing substituent at C2 were found to undergo a cascade consisting of 6-endo cyclization and a subsequent pinacol-type shift [37][98]. Since the 5-endo cyclizations discussed above most likely proceed through cationic intermediates, external nucleophiles were shown to trap these intermediates at C1 in

• the case with gold-catalyzed cyclizations, the competing elimination through loss of a proton could not be entirely prevented. For example, a methoxyiodocarbocyclization of 27 occurred in 22% yield when the iodocyclization was run in methanol. Additionally, the developing positive charge can be

A comparative study of the Au-catalyzed cyclization of hydroxy-substituted allylic alcohols and ethers

• Berenger Biannic,
• Thomas Ghebreghiorgis and
• Aaron Aponick

Beilstein J. Org. Chem. 2011, 7, 802–807, doi:10.3762/bjoc.7.91

• ]. Herein we report a study of Au-catalyzed cyclizations with different leaving groups that do not require deprotection, and data on the reaction progress that allows comparison between leaving groups and cis- versus trans-olefins. Results and Discussion At the outset, one of the important goals was to be

Solvent- and ligand-induced switch of selectivity in gold(I)-catalyzed tandem reactions of 3-propargylindoles

• Estela Álvarez,
• Delia Miguel,
• Patricia García-García,
• Manuel A. Fernández-Rodríguez,
• Félix Rodríguez and
• Roberto Sanz

Beilstein J. Org. Chem. 2011, 7, 786–793, doi:10.3762/bjoc.7.89

• of 3-propargylindoles. Keywords: catalysis; gold; indoles; Nazarov cyclizations; selectivity; Introduction Catalysis with gold complexes as carbophilic π-acids has become a highly developed area in the last decade [1][2][3][4][5][6][7]. In particular, 1,2-acyl migration reactions of propargylic

• present at either of these positions, they undergo further cyclizations to afford 3-(inden-2-yl)indoles 3 or 4 (Scheme 1). An analysis of the aromaticity of the transition state structures for these cyclizations by DFT calculations revealed that these electrocyclic ring closures could be considered as

Alkene selenenylation: A comprehensive analysis of relative reactivities, stereochemistry and asymmetric induction, and their comparisons with sulfenylation

• Vadim A. Soloshonok and
• Donna J. Nelson

Beilstein J. Org. Chem. 2011, 7, 744–758, doi:10.3762/bjoc.7.85

• ], which are analogous to areneselenenyl compounds 1 [32][33][34][35][36][37][38][39][40][41][42][43]. Data in Table 7 compare electrophilic cyclizations of alkenes by using compound 1 (X = OTf) [32][33][34][35][36][37][38][39][40][41][42][43][91] and compound 10, which is the sulfur analog of the chiral

• of 1 and 2 with alkenols in Scheme 2 at −78 °C. Energy increase in 9 upon substitution at the α position [34]. Alkene IEs (eV), relative rates (krel), and log krel values of PhSCl addition to olefins. Electrophilic cyclizations of alkenes with electrophiles 1 (X = OTf) and 10. Supporting Information

Gold-catalyzed heterocyclizations in alkynyl- and allenyl-β-lactams

• Benito Alcaide and
• Pedro Almendros

Beilstein J. Org. Chem. 2011, 7, 622–630, doi:10.3762/bjoc.7.73

• which rely on the activation of the allene and alkyne component. The mechanism as well as the regio- and stereoselectivity of the cyclizations are also discussed. Keywords: alkynes; allenes; gold; heterocyclizations; β-lactams; Introduction The chemistry of alkynes and allenes has been extensively

• (endo versus exo cyclizations) as well as it being one of the most rapid and convenient methods for the preparation of heterocycles. On the other hand, in addition to the key role that β-lactams play in medicinal chemistry, namely, their action against pathogenic bacteria, enzyme inhibition, or gene

• mechanism as well as the regio- and stereoselectivity of the cyclizations are also discussed. Review Gold-catalyzed heterocyclizations in allenyl-β-lactams Aminocyclizations The AuCl3-catalyzed cyclization of 4-allenyl-2-azetidinones affords bicyclic β-lactams [31]. The former were prepared by the selective

Construction of cyclic enones via gold-catalyzed oxygen transfer reactions

• Leping Liu,
• Bo Xu and
• Gerald B. Hammond

Beilstein J. Org. Chem. 2011, 7, 606–614, doi:10.3762/bjoc.7.71

• reported gold-catalyzed cyclizations to cyclohexenones 17, employing terminal 1,6-diynes 16 as substrates in the presence of a Brønsted acid and 1 equiv of water (Scheme 12) [48]. None of the desired products were obtained in the absence of the gold catalyst, the Brønsted acid or water. Interestingly, when

• these transformations were also comparatively discussed. Similar Brønsted acid or other metal mediated transformations and their applications to cascade cyclizations were additionally described. Given gold’s strong π-electrophilicity, it is expected that novel applications of gold catalysts in reactions

• cyclization of alkynyl ketones. Gold-catalyzed cyclization of terminal alkynyl ketones. Gold-catalyzed tandem oxygen transfer/Nazarov cyclizations. TfOH-mediated cyclization of alkynyl ketones. Gold-catalyzed cyclizations of 2-alkynyl-1,5-diketones. Designed isotopic labeling experiment for mechanistic

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

• selectivity using the Utimoto conditions to prepare 6,6-spiroketals. Therefore, he suggested the preferred use of Ziese’s dimer, a platinum catalyst (Scheme 3, Reaction 2), for such cyclizations [9]. In an unrelated study that also bears on the current work, Aponick and co-workers described a gold-catalyzed

Synthesis of 5-(2-methoxy-1-naphthyl)- and 5-[2-(methoxymethyl)-1-naphthyl]-11H-benzo[b]fluorene as 2,2'-disubstituted 1,1'-binaphthyls via benzannulated enyne–allenes

• Yu-Hsuan Wang,
• Joshua F. Bailey,
• Jeffrey L. Petersen and
• Kung K. Wang

Beilstein J. Org. Chem. 2011, 7, 496–502, doi:10.3762/bjoc.7.58

• '-disubstituted 1,1'-binaphthyls with the newly constructed benzofluorenyl group serving as a naphthyl moiety. Keywords: benzannulated enediynyl alcohols; benzannulated enyne–allenes; 2,2'-disubstituted 1,1'-binaphthyls; 5-(1-naphthyl)-11H-benzo[b]fluorenes; Schmittel cascade cyclizations; Introduction

Molecular rearrangements of superelectrophiles

• Douglas A. Klumpp

Beilstein J. Org. Chem. 2011, 7, 346–363, doi:10.3762/bjoc.7.45

• developed. Among the useful Friedel–Crafts reactions, a large number of cyclizations have been developed, including efficient routes to heterocyclic systems [12]. Several reports have also described superelectrophiles participating in concerted reactions, such as the Nazarov cyclization [13]. Because

• migrations or hydride shifts. Simple Friedel–Crafts type reactions and cyclizations will not be covered. Review Ring opening reactions Several types of superelectrophiles are known to undergo ring opening reactions. The ring opening reaction step can be followed by the reaction with a nucleophile. For

Ene–yne cross-metathesis with ruthenium carbene catalysts

• Cédric Fischmeister and
• Christian Bruneau

Beilstein J. Org. Chem. 2011, 7, 156–166, doi:10.3762/bjoc.7.22

• later Mori [22][23] utilized chromium alkoxycarbene to develop the first cyclizations via catalytic intramolecular enyne metathesis transformation. These initial works gave reason to postulate the interaction of metal carbene with alkyne to form a metallacyclobutene that rearranges to give a metal

Highly substituted benzannulated cyclooctanol derivatives by samarium diiodide-induced cyclizations

• Jakub Saadi,
• Irene Brüdgam and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2010, 6, 1229–1245, doi:10.3762/bjoc.6.141

• -endo-trig cyclizations. Efficacy, regioselectivity and stereoselectivity of these reactions via samarium ketyls strongly depend on the substitution pattern of the attacked alkene moiety. The stereoselectivity of the protonation of the intermediate samariumorganyl is also influenced by the structural

• -trig cyclizations to cycloheptanol derivatives have been observed. In examples with high steric hindrance the ketyl–aryl coupling can be a competing process. Keywords: cyclooctanes; ketones; ketyls; medium-sized rings; samarium diiodide; single electron transfer; styrene derivatives; radicals

• ][7][8][9][10][11][12][13][14][15][16][17][18]. Successful approaches include ring-closing metathesis [4], rearrangements [5], and cycloadditions [6], transition metal-catalyzed cyclizations [7][8], nucleophilic and electrophilic substitution reactions [9] as well as ring expansion reactions [10

A new and facile synthetic approach to substituted 2-thioxoquinazolin-4-ones by the annulation of a pyrimidine derivative

• Nimalini D. Moirangthem and
• Warjeet S. Laitonjam

Beilstein J. Org. Chem. 2010, 6, 1056–1060, doi:10.3762/bjoc.6.120

• of various fused heterocyclic compounds. In recent years, we have reported one-pot cyclizations of DTBA with hydrazine [23][24], hydroxylamine [25], guanidine [26], etc. In addition, one-pot cyclizations of DTBA-derived arylidenes have also been reported. Recently, we reported the synthesis of fused

Total synthesis of (±)-coerulescine and (±)-horsfiline

• Mukund G. Kulkarni,
• Attrimuni P. Dhondge,
• Sanjay W. Chavhan,
• Ajit S. Borhade,
• Yunnus B. Shaikh,
• Deekshaputra R. Birhade,
• Mayur P. Desai and
• Nagorao R. Dhatrak

Beilstein J. Org. Chem. 2010, 6, 876–879, doi:10.3762/bjoc.6.103

• radical cyclizations [20][21][22][23][24], electrophilic cyclization [25], asymmetric nitroolefination reaction [26], palladium asymmetric allylic alkylation [27], palladium-catalyzed domino Heck–cyanation [28], Pd-catalyzed intramolecular cyanoamidation [29][30], NHC-mediated O- to C-carboxyl transfer

Novel tetracyclic structures from the synthesis of thiolactone-isatin hybrids

• Renate Hazel Hans,
• Hong Su and
• Kelly Chibale

Beilstein J. Org. Chem. 2010, 6, No. 78, doi:10.3762/bjoc.6.78

• indicated by X-ray crystallographic data. The absence of the other diastereomer may be due to destabilizing steric interactions with the carbonyl group of the amide and the oxygen of the vinyl ether. Similar cyclizations leading to bridged lactams have been reported [43][44]. Synthesis of tetracycles 4 was

Addition of lithiated enol ethers to nitrones and subsequent Lewis acid induced cyclizations to enantiopure 3,6-dihydro-2H-pyrans – an approach to carbohydrate mimetics

• Fabian Pfrengle and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2010, 6, No. 75, doi:10.3762/bjoc.6.75

• efficient preparation include Prins cyclizations, intramolecular substitutions, ring closure metathesis, and hetero Diels–Alder reactions [1][2]. Our group recently reported the synthesis of enantiopure aminopyrans employing as the key step a Lewis acid induced rearrangement of 1,2-oxazines to bicyclic

• suitable substrates for Lewis-acid induced cyclizations furnishing mono-, di-, or spirocyclic dihydropyrans. Subsequent reactions such as bromination, acidic hydrolysis or dihydroxylation provided differently substituted and configured pyranone derivatives as precursors for the stereoselective synthesis of

Preparation of pyridine-3,4-diols, their crystal packing and their use as precursors for palladium-catalyzed cross-coupling reactions

• Tilman Lechel,
• Irene Brüdgam and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2010, 6, No. 42, doi:10.3762/bjoc.6.42

• extended π-systems using palladium-catalyzed coupling reactions. Moreover, compounds 4b–c show interesting photophysical properties that might be thoroughly investigated in the future. The 3,4-dialkynyl-pyridine derivatives 4 or 5 are also candidates for Bergman cyclizations [34][35] which may establish a

Reduction of arenediazonium salts by tetrakis(dimethylamino)ethylene (TDAE): Efficient formation of products derived from aryl radicals

• Mohan Mahesh,
• John A. Murphy,
• Franck LeStrat and
• Hans Peter Wessel

Beilstein J. Org. Chem. 2009, 5, No. 1, doi:10.3762/bjoc.5.1

• substrates, to syntheses of indolines and indoles. Cascade radical cyclizations of aryl radicals derived from arenediazonium salts are also reported. The relative ease of removal of the oxidized by-products of TDAE from the reaction mixture makes the methodology synthetically attractive. Keywords

• of these cyclizations is the ease of purification of the product from the reaction mixture. The oxidized product of TDAE, namely octamethyloxamidinium bis(tetrafluoroborate) (21), was easily removed either by filtration or by simple work-up with water. Cascade cyclizations To determine the scope of

• cascade radical cyclizations to afford the bicyclized product 47 in 85% and 77% yield respectively (Scheme 5). The ability of TDAE to mediate such efficient cascade cyclizations via two C-C bond formations reactions in one pot from the aryl radical 45 was significant considering the fact that our previous

Synthesis of 2,3,6,7-tetrabromoanthracene

• Christian Schäfer,
• Friederike Herrmann and
• Jochen Mattay

Beilstein J. Org. Chem. 2008, 4, No. 41, doi:10.3762/bjoc.4.41

• . Keywords: anthracene; arenes; cyclizations; polycycles; ring closure; 2,3,6,7-tetrabromoanthracene; Introduction Anthracene and its derivatives are long known polycyclic aromatic compounds showing a high potential for use in materials science (e.g. fluorescence probing, photochromic systems

Sordarin, an antifungal agent with a unique mode of action

• Huan Liang

Beilstein J. Org. Chem. 2008, 4, No. 31, doi:10.3762/bjoc.4.31

• sordarin [17] in 2004 and 2006, respectively. Both Kato’s and Mander’s syntheses employed intramolecular Diels-Alder cyclizations to construct the norbornene-like framework, while an intramolecular Pd catalyzed Tsuji-Trost reaction was utilized by the Narasaka group to build the diterpene core. Kato’s

Dimerization of propargyl and homopropargyl 6-azido- 6-deoxy- glycosides upon 1,3-dipolar cycloaddition

• Nikolas Pietrzik,
• Daniel Schmollinger and
• Thomas Ziegler

Beilstein J. Org. Chem. 2008, 4, No. 30, doi:10.3762/bjoc.4.30

• rings containing two sugar moieties and two 1,2,3-triazole moieties. For instance, such compounds may function as novel ligands for the preparation of metal complexes [24]. Further examples for cyclizations of other azido-alkynyl-glycosides are under investigation. Schematic representation of

Allylsilanes in the synthesis of three to seven membered rings: the silylcuprate strategy

• Asunción Barbero,
• Francisco J. Pulido and
• M. Carmen Sañudo

Beilstein J. Org. Chem. 2007, 3, No. 16, doi:10.1186/1860-5397-3-16

• silylcuprate with electrophiles ("the silylcuprate strategy") provides new routes for the synthesis of functionalised allylsilanes, which undergo highly stereocontrolled silicon-assisted intramolecular cyclizations leading to three to seven membered ring-formation. Background Organosilicon compounds and in

• to a wide range of functionalised allylsilanes, which are valuable intermediates for carbocyclic annulations. Effectively, the former substrates (containing a nucleophilic allylsilane unit and an electrophilic function) undergo "intramolecular allylsilane terminated" cyclizations when treated with

• reaction between 2 and α,β-unsaturated acid chlorides provides an easy approach to silylated divinyl ketones 9–10 (Scheme 2), which are excellent precursors for silicon-directed Nazarov cyclizations. Acid catalysed electrocyclic closure (TFA, 0–20°C) allows the formation of exocyclic 2-methylenecyclopentan

Do α-acyloxy and α-alkoxycarbonyloxy radicals fragment to form acyl and alkoxycarbonyl radicals?

• Dennis P. Curran and
• Tiffany R. Turner

Beilstein J. Org. Chem. 2006, 2, No. 10, doi:10.1186/1860-5397-2-10

• through mesylates by a standard procedure. Iodides 11a and 11b were stable to heating at 120°C in C6D6 for 24 h, so polar pathways for product formation are not likely in the cyclization experiments described below. The projected mechanism for cyclizations of 11a,b with Bu3SnH in a competition kinetics

• ultimately also result in the formation of 15, but the concentration dependence of this process is not clear since the oxidation step is not fully understood. Based on the mechanism in Figure 4, authentic samples of all products expected from the cyclizations of 11a and 11b were synthesized as shown in

• process begins to break down, so low conversions and yields result. AIBN has been suggested to be an oxidant in related reactions, [9][33] so we conducted a series of individual cyclizations of 11a at 0.01 M with increasing amounts of AIBN. The results of these experiments are summarized in Table 2. If

Efficient synthesis of 5-substituted 2-aryl- 6-cyanoindolizines via nucleophilic substitution reactions

• Eugene V. Babaev,
• Natalya I. Vasilevich and
• Anna S. Ivushkina

Beilstein J. Org. Chem. 2005, 1, No. 9, doi:10.1186/1860-5397-1-9

• open a new way to functionalize the C-5 position (in most cases considered as inactive). The studies of further cyclizations of 5-substituted indolizines involving neighbouring cyano-group and ring position C3 is underway. Note *Characteristics of parent indolizinones 1 a – d were identical to those

Synthesis of 2,6-trans- disubstituted 5,6-dihydropyrans from (Z)-1,5-syn-endiols

• Eric M. Flamme and
• William R. Roush

Beilstein J. Org. Chem. 2005, 1, No. 7, doi:10.1186/1860-5397-1-7

• dihydropyan ent-3. Cyclic ethers of various ring size have been synthesized by the cyclodehydration of diols through the use of oxyphosphonium salts and phosphorane reagents.[18][19][20][21][22][23] We reasoned that because the rate determining step of these cyclizations is believed to be the nucleophilic