Reduction of benzylic alcohols and α-hydroxycarbonyl compounds by hydriodic acid in a biphasic reaction medium

• Michael Dobmeier,
• Josef M. Herrmann,
• Dieter Lenoir and
• Burkhard König

Beilstein J. Org. Chem. 2012, 8, 330–336, doi:10.3762/bjoc.8.36

• position (Table 1, entries 4 and 6) and aromatic hydroxy groups (Table 2, entry 7) or aromatic ethers (Table 1, entry 5) were not affected. Moreover, heterocycles such as thiophene (Table 1, entry 7) were stable under these conditions whereas furans (Table 1, entry 8) were decomposed due to ring opening

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

• form 6–8-membered rings [29][30][31]. A similar reaction can also be carried out with GaCl3 [32] and Pt(II) [33] as catalysts. In contrast, alkynyl furans react with gold to give phenols by using Au(III), Au(I) [1][2][34][35][36][37], or Pt(II) as the catalyst [38][39]. In our efforts towards the

Combined directed ortho-zincation and palladium-catalyzed strategies: Synthesis of 4,n-dimethoxy-substituted benzo[b]furans

• Verónica Guilarte,
• M. Pilar Castroviejo,
• Estela Álvarez and
• Roberto Sanz

Beilstein J. Org. Chem. 2011, 7, 1255–1260, doi:10.3762/bjoc.7.146

• , give rise to new and interesting dimethoxy-substituted benzo[b]furans. Keywords: benzo[b]furans; o-zincation; palladium; selectivity; Introduction The directed ortho-metallation (DoM) reaction has been widely used as a powerful and efficient method for regioselective functionalization of aromatic

• . However, their application to the synthesis of 4-substituted benzo[b]furans is especially challenging, because the meta-substituted starting materials tend to cyclize at the less hindered ortho-position, leading to the formation of 6-substituted heterocycles or a mixture of 6- and 4-substituted ones [32

• 2,3-difunctionalized phenol derivatives were applied to the synthesis of 4-functionalized benzo[b]furans [39], 4- or 7-alkoxyindoles [40], and 7-oxy-substituted benzo[b]thiophenes [41] by employing Pd-catalyzed cross-coupling reactions or halocyclization processes. Following our interest in the

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

• by our smooth glyoxylation–alkynylation sequences with a variety of unfunctionalized π-nucleophiles, such as pyrazoles, thiophenes, furans, and even the hydrocarbon azulene (1a) [53], we decided to perform optimization studies of the glyoxylation–decarbonylative alkynylation with guaiazulene (1b), a

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

• intermediates that undergo subsequent intermolecular annulations with diverse partners. For example, in 2008, L. Zhang and coworkers demonstrated that a series of 1-(1-alkynyl)cyclopropyl ketones 8, previously used by Schmalz for the synthesis of furans [44], can be used as precursors of reactive intermediates

• -catalyzed synthesis of polycyclic, fully substituted furans from 1-(1-alkynyl)cyclopropyl ketones [45]. Gold-catalyzed 1,3-dipolar cycloaddition of 2-(1-alkynyl)-2-alken-1-ones with nitrones [47]. Enantioselective 1,3-dipolar cycloaddition of 2-(1-alkynyl)-2-alken-1-ones with nitrones [48]. Gold-catalyzed

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

• strategy to construct furan analogues. Du et al. reported a highly efficient Au-catalyzed cyclization of (Z)-enynols that proceeded under mild reaction conditions. This methodology provided rapid access to substituted furans 6 and stereo-defined (Z)-5-ylidene-2,5-dihydrofurans 7 in a regioselective manner

• from suitably substituted (Z)-2-en-4-yn-1-ols 5 [20]. A similar strategy has been applied to an efficient formation of substituted furans 9 through gold-catalyzed selective cyclization of enyne-1,6-diols 8 [21]. Nucleophilic attack of the hydroxy oxygen atom on 1-position to a gold-coordinated C–C

• triple bond formed the vinyl–gold complex. Surprisingly, no other cyclic compound formed by nucleophilic attack of the hydroxy oxygen atom on C-6-position to a gold-coordinated C–C triple bond was formed. A new efficient route to furans 11 by gold-catalyzed intramolecular nucleophilic attack of readily

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

• Florin M. Istrate Fabien Gagosz Département de Chimie, UMR 7652, CNRS/Ecole Polytechnique, 91128 Palaiseau, France 10.3762/bjoc.7.100 Abstract A series of ynenyl allyl ethers were rearranged into polysubstituted furans in the presence of a gold(I) catalyst. It is proposed that the transformation

• involves a Claisen-type rearrangement that allows the efficient creation of quaternary centers under mild experimental conditions. Keywords: Claisen rearrangement; furans; gold-catalysis; quaternary centers; Findings Furans represent an important class of heteroaromatic compounds, which are found in a

• precursors for the formation of polysubstituted furans in the presence of a gold(I) or a gold(III) catalyst [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44]. We report herein our own investigations in this field which have led to the development

Gold-catalyzed propargylic substitutions: Scope and synthetic developments

• Olivier Debleds,
• Eric Gayon,
• Emmanuel Vrancken and
• Jean-Marc Campagne

Beilstein J. Org. Chem. 2011, 7, 866–877, doi:10.3762/bjoc.7.99

• of the homopropargylic alcohol on the triple bond or a gold-catalyzed rearrangement of a transient epoxide as recently described by Blanc and Pale [74][75][76]. Synthetic developments This result prompted us to explore the synthesis of functionalized furans from various homopropargylic alcohols

• homopropargylic alcohol is protected as a MOM ether, a mixture of furans resulting from proto-demetallation 35 and MOM transfer 36 was obtained in a 75:25 ratio, respectively, whereas in the presence of gold(I) catalyst the proto-demetallation product 35 was the sole product. For related cyclization with

• . Isoxazolines formation. Addition of nucleophiles to isoxazolines. Potential mechanistic pathways. Synthesis of furans from homoproargylic alcohols. Synthesis of furans. Propargylic substitutions: Synthetic applications. GH2 = Grubbs–Hoveyda 2nd generation catalyst. Catalyst screening. Propargylic N

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

• intermediates will most likely never be matched by electrophilic analogues and will be unique tools for the creation of valuable target compounds. Mechanistic scenarios for alkyne activation. Synthesis of 3(2H)-furanones. Synthesis of furans. Formation of dihydrooxazoles. Variation on indole formation

High chemoselectivity in the phenol synthesis

• Matthias Rudolph,
• Melissa Q. McCreery,
• Wolfgang Frey and
• A. Stephen K. Hashmi

Beilstein J. Org. Chem. 2011, 7, 794–801, doi:10.3762/bjoc.7.90

• phenol synthesis are much faster than the steps of the interception reaction. In the latter the barrier of activation is higher. At the same time this explains the high tolerance of this very efficient and general reaction towards functional groups. Keywords: alcohols; alkenes; alkynes; furans; gold

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

• 24 to give 3-chromanol 25, which was reported by He and co-workers in 2004 (Scheme 8) [25]. The same year, Hashmi and co-workers described the first example of a gold-catalyzed conversion of alkynyl epoxides 26 into furans 27 [26][27]. Mechanistic studies performed later by Pale and co-workers [28

• . Acyloxylated alkynyl oxiranes 28 and 30 have also proved to be versatile building blocks for the synthesis of divinyl ketones 29 [29], 2,5-disubstituted furans 31 [30] and difurylmethane derivatives 32 [31], respectively (Scheme 10). Epoxy alkynes can also be transformed with high stereoselectivity into ketals

• nucleophilic oxidant in this context [40]. The gold-catalyzed intramolecular nucleophilic attack of heteroatoms on alkynes, followed by ring expansion, represents an appropriate method for the synthesis of furans and pyrroles. In 2006, Schmalz and co-workers reported a gold-catalyzed cascade reaction of

When cyclopropenes meet gold catalysts

• Frédéric Miege,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2011, 7, 717–734, doi:10.3762/bjoc.7.82

• discussed by the authors (Scheme 17) [18]. It is worth noting that for substrates bearing two electron-withdrawing groups at C3 (COMe and CO2Me), no gold-catalyzed rearrangement took place under similar conditions. However, such cyclopropenes have been converted to furans in the presence of CuI or PdCl2

• was unreactive under these conditions (Scheme 22) [17]. Intermolecular cyclopropanation of furans: Synthesis of conjugated trienes In 2011, Lee and Hadfield reported the synthesis of conjugated trienes by gold-catalyzed intermolecular reaction of cyclopropenes with furans [24]. Several catalysts such

• (Scheme 24) [24]. Other mono- or disubstituted furans can be successfully used as partners, as illustrated by the gold-catalyzed reactions involving 3-tert-butyl-3-methylcyclopropene as substrate that led to the corresponding tetra- or pentasubstituted trienes of type 57 or triene 58 bearing two geminal

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

• cyclocondensation of alkyne diols to give substituted furans (Scheme 3, Reaction 3) [35]. Our objective, laid out in Scheme 4, was to initiate cycloisomerization with a 5-endo-dig cyclization of the homopropargyl alcohol 6, followed by 5-exo-trig cyclization onto the resulting dihydrofuran, whilst avoiding

Formation of macrocyclic lactones in the Paternò–Büchi dimerization reaction

• Junya Arimura,
• Tsutomu Mizuta,
• Yoshikazu Hiraga and
• Manabu Abe

Beilstein J. Org. Chem. 2011, 7, 265–269, doi:10.3762/bjoc.7.35

• : furans; macrocyclic lactone; oxetane; Paternò–Büchi reaction; photochemical reaction; Findings Photochemical [2 + 2] cycloaddition reaction of alkenes with carbonyls, so-called Paternò–Büchi reaction [1][2][3][4][5][6][7][8][9][10][11][12][13], is one of the most efficient methods for preparing

First synthesis of 2-(benzofuran-2-yl)-6,7-methylene dioxyquinoline-3-carboxylic acid derivatives

• Wentao Gao,
• Jia Liu,
• Yun Jiang and
• Yang Li

Beilstein J. Org. Chem. 2011, 7, 210–217, doi:10.3762/bjoc.7.28

• -arylpropenoic acids to yield 2-methyl, 2-carboxy, and 2-arylbenzo[b]furans, respectively [40]. However, these methods often require expensive catalysts and/or multi-step syntheses. Herein, we demonstrate an attractive one-pot procedure to afford the desired 2-(benzofuran-2-yl)-6,7-methylenedioxyquinoline-3

Photocycloaddition of aromatic and aliphatic aldehydes to isoxazoles: Cycloaddition reactivity and stability studies

• Axel G. Griesbeck,
• Marco Franke,
• Jörg Neudörfl and
• Hidehiro Kotaka

Beilstein J. Org. Chem. 2011, 7, 127–134, doi:10.3762/bjoc.7.18

• of this reaction [6]. Previous publications have clearly demonstrated the versatility of the Paternò–Büchi reaction in various synthetic applications which gives rise to a multiplicity of different products. The photocycloaddition of furans to carbonyl compounds affords the corresponding β-hydroxy

• reagent on the liberated benzaldehyde. Conclusion The photocycloaddition of electronically excited carbonyl compounds to isoxazoles is clearly less effective than with other five-membered aromatic or non-aromatic heterocycles (furans, thiophenes, pyrroles, oxazoles, dihydrofurans, dihydropyrroles) [1

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

• -isomers [87]. Unlike pyrroles, furan, thiophene and selenophene react with CF3SCl only in the presence of catalysts. For selenophene [84] and thiophenes [85] SnCl4 is sufficient, whilst furans require more forcing conditions usually involving prolonged heating (20 h at 60 °C) and in pyridine for

A novel and efficient method to prepare 2-aryltetrahydrofuran-2-ylphosphonic acids

• Vsevolod V. Komissarov,
• Anatoly M. Kritzyn and
• Jouko J. Vepsäläinen

Beilstein J. Org. Chem. 2010, 6, No. 63, doi:10.3762/bjoc.6.63

• [18]. The length of hydrocarbon chain is also of major importance, since cyclic tetrahydropyran derivatives are not formed in the case of arylpentanones 9a,b under the same conditions as those used for the synthesis of furans 2 (Scheme 3). According to the NMR spectra, the only phosphorus containing

• -aryl-1-butanones 1 with PCl3/AcOH lead to unexpected cyclic product 2 instead of the expected alkene 3. Preparation of cyclic furans 2a–e and ethyl esters 4a,c from chloroarylbutanones 1. Proposed reaction mechanism for the cyclization reaction. Acyclic products are obtained from pentanones 9a,b and

A review of new developments in the Friedel–Crafts alkylation – From green chemistry to asymmetric catalysis

• Magnus Rueping and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2010, 6, No. 6, doi:10.3762/bjoc.6.6

• and with good ortho/para selectivity. Although different arenes and heteroarenes, including thiophene can be efficiently alkylated, furans did not result in the desired products. In addition to styrene, dihydronaphthalene and α-methylstyrene could be used as electrophiles. In the latter case, the

• indoles, thiophenes, pyrroles or furans gave the desired anti-1,1,2-triarylalkanes 110 in good yields and with high diastereoselectivities (Scheme 40B). BF3•OEt2 and TFA were used in stoichiometric amounts to promote this reaction. However, application of BF3 resulted in significantly higher reactivity

End game strategies towards the total synthesis of vibsanin E, 3-hydroxyvibsanin E, furanovibsanin A, and 3-O-methylfuranovibsanin A

• Brett D. Schwartz,
• Craig M. Williams and
• Paul V. Bernhardt

Beilstein J. Org. Chem. 2008, 4, No. 34, doi:10.3762/bjoc.4.34

• methylated furans using catalytic amounts of mercury triflate. Although verification of this protocol was undertaken on a cycloheptanone derivative, substrate 39 failed to give the desired furan 42 (Scheme 6). Instead, hydration was observed as the major reaction pathway (i.e. 40) with furan 41 being

Trapping evidence for the thermal cyclization of di-(o-acetylphenyl)acetylene to 3,3'-dimethyl- 1,1'-biisobenzofuran

• Charles P. Casey,
• Neil A. Strotman and
• Ilia A. Guzei

Beilstein J. Org. Chem. 2005, 1, No. 18, doi:10.1186/1860-5397-1-18

• electrocyclic ring closures to furans.[9][17][18] Related ring closures of o-acyl phenylcarbenes to isobenzofurans have been reported (Scheme 9).[19][20][21] These carbenes were formed as transient intermediates by photolytic or chemical cleavage of diazo or diazirine compounds. Isobenzofurans formed in this