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

• )-catalyzed intermolecular (2 + 2) cycloaddition of alkynes with alkenes [62]. Metal-catalyzed cycloaddition of alkynes tethered to cycloheptatriene [65]. Gold-catalyzed cycloaddition of functionalized ketoenynes: Synthesis of (+)-orientalol F [68]. Gold-catalyzed intermolecular cyclopropanation of enynes

• with alkenes [70]. Gold-catalyzed intermolecular hetero-dehydro Diels–Alder cycloaddition [72]. Gold(I)-catalyzed stereoselective olefin cyclopropanation [74]. Reaction of propargylic benzoates with α,β-unsaturated imines to give azepine cycloadducts [77]. Gold-catalyzed (3 + 3) annulation of

Scalable synthesis of (1-cyclopropyl)cyclopropylamine hydrochloride

• Sergei I. Kozhushkov,
• Alexander F. Khlebnikov,
• Rafael R. Kostikov,
• Dmitrii S. Yufit and
• Armin de Meijere

Beilstein J. Org. Chem. 2011, 7, 1003–1006, doi:10.3762/bjoc.7.113

• cyclopropyl cyanide [3][4][5][6][7][8][9][10][11][12][13] by application of the Szymoniak–Kulinkovich reductive cyclopropanation procedure [14][15]. In our hands, however, this patented protocol [3][4][5][6][7][8][9][10][11][12][13] provided poor yields (15–20%) of impure 4 [16], which had to be purified by

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

• the presence of an Au catalyst to afford the cyclopropanation product 70 with excellent diastereoselectivity. This is only one example where gold catalysts open the door to a realm of reactivity that traditional electrophiles can never reach. Conclusion This review was intended to demonstrate that

• cyclization modes for 1,5-enynes. Iodine-induced cyclization of 1,5-enynes. Diverse reactivity of 1,6-enynes. Iodocyclization of 1,6-enynes. Cyclopropanation of alkenes with 1,6-enynes. Cyclopropanation of alkenes with 1,6-enynes. Acknowledgements S. H. thanks the Erasmus programme for supporting her visit

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

• second option would be a classical cyclopropanation of an olefin. A third option would be trapping of intermediate A with an intramolecular hydroxy nucleophile [36]. Here we report our observations when trying to apply these principles to intermediates of type A or B. Results and Discussion

• in an intramolecular manner. Substrate 8 could potentially undergo three different modes of reaction (Scheme 4). After the initial step, the intermediate E would be produced (analogous to A). Cyclopropanation of the styrene subunit by the cyclopropyl carbenoid would deliver 9. If E rearranged to the

• vinylcarbenoid F, the two competing reactions would be the formation of the phenol 10 and cyclopropanation to form 11. The synthesis of 8 was possible by a short route (Scheme 5). Starting from the commercially available 2-bromostyrene (12), a halogen–metal exchange and subsequent formylation according to a

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

• . Cyclopropanes 85a are generated in situ by intermolecular cyclopropanation of enyne 84 and a carbene resulting from the rearrangement of propargyl ester 83. When tertiary propargyl esters are used, the 5-endo-dig cyclization generates the carbocation 89. Migration of the pivaloyloxy group affords the allylic

• -catalyzed synthesis of ventricos-7(13)-ene. 1,2- vs 1,3-Carboxylate migration. Gold-catalyzed cycloisomerization of vinyl alkynyl cyclopropanes. Proposed mechanism for the cycloisomerization of vinyl alkynyl cyclopropanes. Gold-catalyzed 1,2-acyloxy rearrangement/cyclopropanation/cycloisomerization cascades

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

• nucleophilic addition with, e.g., alcohols, arenes or carbonyl groups, undergo self- or cross-carbene couplings and bring about the cyclopropanation of olefins. The first of these reaction types is often considered to be representative of cationic intermediates whereas the other two are best ascribed to

• in this review, these structural effects were found to have important consequences in terms of reactivity in the case of intermolecular olefin cyclopropanation promoted by gold carbenes generated from cyclopropenes. In fact, the first reports on gold-catalyzed reactions involving cyclopropenes

• cyclopropenes examined so far in this review have involved capture of the organogold intermediates, resulting from electrophilic activation and ring-opening, by an external or an internal nucleophile. Cyclopropanation of olefins, a reaction classically attributed to the carbene-like reactivity, will now be

Gold-catalyzed naphthalene functionalization

• Pedro J. Pérez,
• M. Mar Díaz-Requejo and
• Iván Rivilla

Beilstein J. Org. Chem. 2011, 7, 653–657, doi:10.3762/bjoc.7.77

• derivatives, formed by the cyclopropanation of one of the double bonds of the naphthalene ring. Later, Müller and co-workers [9] showed the effect of a series of Rh2(L-L)4 in the same transformation but with ethyl diazoacetate as the carbene source. A mixture of the products (2a–d) arising from

• cyclopropanation, ring opening and the formal insertion of CHCO2Et into the aromatic C–H bonds were observed, with 2a being by far the major product (Scheme 2). In the course of our research, focussed on the development of group 11 metal-based catalysts for carbene transfer reactions from diazo compounds [10], we

• formed, identified as ethyl 1a,7b-dihydro-1H-cyclopropa[a]naphthalene-1-carboxylate (2a), i.e., the product derived from the direct cyclopropanation of the naphthalene C–C double bond (Scheme 4a). By contrast, the use of the gold catalyst IPrAuCl (1b) under the same reaction conditions gave a mixture of

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

• . This procedure has been successfully used to prepare C-aryl glycoside from C-alkynyl glycoside and ethylene according to an EYCM/Diels–Alder/oxidation sequence (Scheme 6) [52][53]. The selective cyclopropanation of the most electron deficient double bond of the unsymmetrical dienic system has been

Tandem catalysis of ring-closing metathesis/atom transfer radical reactions with homobimetallic ruthenium–arene complexes

• Yannick Borguet,
• Xavier Sauvage,
• Guillermo Zaragoza,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2010, 6, 1167–1173, doi:10.3762/bjoc.6.133

• ][13][14], ATRP [15][16][17][18], cyclopropanation [19], dihydroxylation [20], hydrogenation [21][22][23], hydrovinylation [24], isomerization [25][26][27][28], oxidation [29], or Wittig reactions [30], to name just a few [31]. In this contribution, we investigate the tandem catalysis of RCM/ATRC

α,β-Aziridinylphosphonates by lithium amide-induced phosphonyl migration from nitrogen to carbon in terminal aziridines

• David. M. Hodgson and
• Zhaoqing Xu

Beilstein J. Org. Chem. 2010, 6, 978–983, doi:10.3762/bjoc.6.110

• aziridinylphosphonate 3b in 79% yield (Table 1, entry 2). Aziridines 1c and 1d underwent migration smoothly without complications arising from potential allylic deprotonation [33], intramolecular cyclopropanation [11][12] or benzylic deprotonation (entries 3 and 4). Mixed results were obtained when the method was

Bis(oxazolines) based on glycopyranosides – steric, configurational and conformational influences on stereoselectivity

• Tobias Minuth and
• Mike M. K. Boysen

Beilstein J. Org. Chem. 2010, 6, No. 23, doi:10.3762/bjoc.6.23

• depended on the steric demand of the 3-O-substituents. To further probe the impact of the 3-position of the pyranose scaffold, we prepared 3-epimerised and 3-defunctionalised versions of these ligands as well as a 3-O-formyl derivative. Application of these new ligands in asymmetric cyclopropanation

• revealed strong steric and configurational effects of position 3 on asymmetric induction, further dramatic effects of the pyranose conformation were also observed. Keywords: asymmetric synthesis; carbohydrates; copper; cyclopropanation; ligand design; Introduction The design and optimisation of chiral

• ligands were subsequently employed in the asymmetric cyclopropanation [22][23] of styrene (4) with ethyl diazoacetate (5). Our results revealed a strong dependence of the enantioselectivity on both the steric bulk and electronic nature of the O-substituents in ligands 2a–c and 3a–f. Furthermore, the

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

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

• the requisite 5-halopyrrolidinone precursor. 5.5. Cha. Dialkoxytitanacyclopropane addition to imides This methodology provides a very elegant way to install the C9a hydroxyl group, which remains the biggest challenge of mitomycin synthesis. Based on the precedent of ester cyclopropanation in presence

• of a titanocyclopropane developed by Kulinkovich [116], Cha’s approach to mitomycins involves the intramolecular addition of the same dialkoxytitanacyclopropane to an imide [117]. In contrast to the Kulinkovich’s cyclopropane synthesis, the imide proved to be resistant to cyclopropanation and the

Asymmetric reactions in continuous flow

• Xiao Yin Mak,
• Paola Laurino and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2009, 5, No. 19, doi:10.3762/bjoc.5.19

• using a silica-supported chiral Co(salen) complex [42]. Asymmetric cyclopropanation has also been studied in continuous flow, using monolithic reactors immobilized with chiral PyBox ligands [43][44]. The cyclopropanation of stryrene with ethyldiazoacetate was investigated as a model reaction for this

• ). Continuous-flow asymmetric cyclopropanation. Continuous asymmetric hydrogenation of dimethyl itaconate in scCO2. Continuous asymmetric transfer hydrogenation of acetophenone. Asymmetric epoxidation using a continuous flow membrane reactor. Enzymatic cyanohydrin formation in a microreactor. Resolution of (R/S

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

• -step pathway involving firstly, Me3Al-catalysed intramolecular cyclization of the oxoallylsilane and subsequent formation of a methylenecyclopentanolate, and then cyclopropanation. This unique mechanism enables the construction of hydroxylated bi-tri- and tetracyclic skeletons, bearing the spiro

• . Intramolecular cyclization of TMS-epoxyallylsilanes. Spiro-cyclopropanation from oxoallylsilanes. Cyclobutane formation from hydroxy-functionalized allysilanes. Cyclobutene formation from vinyltin cuprates and epoxides. Silylcupration of 1,2-propadiene and reaction with α,β-unsaturated nitriles. Cycloheptane