Gold(I)-catalyzed enantioselective cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2013, 9, 2250–2264, doi:10.3762/bjoc.9.264

• could be formally categorized as a [2 + 1] cycloaddition. In particular, they showed that it is possible to trap the intermediate gold–carbenes resulting from a 1,2-acyloxy migration in propargyl esters such as 1, with external alkenes (e.g. vinylarenes), to give cyclopropane products [41]. The racemic

• variant of the method, which employs Ph3PAuCl/AgSbF6 as a catalyst, predominantly affords cis-cyclopropane adducts of type 2, and tolerates a wide range of olefin substituents. Importantly, the authors demonstrated that the process could also be rendered enantioselective by using a chiral bisgold complex

• with high diastereoselectivity. Moreover, the enantioselective cyclopropanation was not limited to arylated olefins (e.g. styrenes), but allyltrimethylsilane also participated in the process, producing the corresponding silylmethyl cyclopropane as a 5:1 mixture of cis:trans isomers with a good 78% ee

A reductive coupling strategy towards ripostatin A

• Kristin D. Schleicher and
• Timothy F. Jamison

Beilstein J. Org. Chem. 2013, 9, 1533–1550, doi:10.3762/bjoc.9.175

• cyclopropane unit had not been previously tested under nickel-catalyzed reductive coupling conditions. Nickel(0) is known to catalyze the rearrangement of vinylcyclopropanes to cyclopentenes; however, activating substituents are commonly required [19][20][21]. Furthermore, application of a proposed 1,5

• the trans double bond in the opening of a cyclopropane with an adjacent hydroxy or mesylate leaving group, regardless of the initial configuration of the cyclopropane (Scheme 3, reaction 2) [27]. Braddock has demonstrated that the internal 3,4-E olefin is obtained exclusively in Prins reactions

• terminated by cyclopropylmethylsilane (Scheme 3, reaction 3), which may be explained by the participation of a carbocation that is stabilized by the adjacent cyclopropane ring in the bisected conformation where (CHOR)R′ is oriented anti to the cyclopropane [28][29][30]. Finally, Micalizio has described a

Copper(II)-salt-promoted oxidative ring-opening reactions of bicyclic cyclopropanol derivatives via radical pathways

• Eietsu Hasegawa,
• Minami Tateyama,
• Ryosuke Nagumo,
• Eiji Tayama and
• Hajime Iwamoto

Beilstein J. Org. Chem. 2013, 9, 1397–1406, doi:10.3762/bjoc.9.156

• ][37][38][39][40][41][42][43][44][45][46][47]. Thus, we believe the reaction follows the pathways shown in Scheme 7 although the possibility of direct formations of 9 and 10, a concerted ET and cyclopropane ring opening, cannot be ruled out. Rapid 5-exo cyclization of hexenyl radical moiety in 9

• from these substrates are strongly influenced by post ring-opening steps. Thus, cyclopropane bond cleavage, which is reversible, does not serve as a product-determining step if a rapid follow-up reaction like hexenyl-radical cyclization does not exist. The results show that by using a proper choice of

Lanostane- and cycloartane-type triterpenoids from Abies balsamea oleoresin

• Serge Lavoie,
• Charles Gauthier,
• Jean Legault,
• Sylvain Mercier,
• Vakhtang Mshvildadze and
• André Pichette

Beilstein J. Org. Chem. 2013, 9, 1333–1339, doi:10.3762/bjoc.9.150

• quaternary carbons, including those at δC 170.8 and 207.6 representing carboxylic and ketone carbonyls, respectively (Table 1). The 1H NMR spectrum showed two doublets at δH 0.35 (J = 3.9 Hz) and 0.52 (J = 3.9 Hz) characteristic of a cyclopropane ring (Table 2), suggesting that 4 is a member of the

Interplay of ortho- with spiro-cyclisation during iminyl radical closures onto arenes and heteroarenes

• Roy T. McBurney and
• John C. Walton

Beilstein J. Org. Chem. 2013, 9, 1083–1092, doi:10.3762/bjoc.9.120

• oxime carbonate, plus 1 equiv of MAP, in t-BuPh or cyclopropane solvent, were irradiated with a 500 W unfiltered Hg lamp directly in the spectrometer resonant cavity. The spectrum obtained from precursor 1f (Figure 2) shows a central 1:1:1 triplet from iminyl radical 5f together with a second species

• saddle points by frequency calculations. The experimental kinetic and spectroscopic data was all obtained in the nonpolar hydrocarbon solvents t-BuPh or cyclopropane. Solvent effects, particularly differences in solvation between the neutral reactants and neutral transition states, were therefore

Study on the total synthesis of velbanamine: Chemoselective dioxygenation of alkenes with PIFA via a stop-and-flow strategy

• Huili Liu,
• Kuan Zheng,
• Xiang Lu,
• Xiaoxia Wang and
• Ran Hong

Beilstein J. Org. Chem. 2013, 9, 983–990, doi:10.3762/bjoc.9.113

• preferentially underwent cyclization to deliver a variety of 3-susbtituted-γ-lactones (25b–d). For comparison, the mCPBA-epoxidation approach in literature always demonstrated that electron-rich alkenes are more reactive leading to the reversal of chemoselectivity [70][71]. A cyclopropane group was also

New reactive intermediates in organic chemistry

• Götz Bucher

Beilstein J. Org. Chem. 2013, 9, 613–614, doi:10.3762/bjoc.9.67

• studies. In order to characterise a reactive intermediate, it had to be trapped. Thus, in order to characterise a carbene, for example, one would intercept it with an alkene and isolate the resulting cyclopropane. Using internal quenchers (molecular clocks) providing well-defined competing reactions

Some aspects of radical chemistry in the assembly of complex molecular architectures

• Béatrice Quiclet-Sire and
• Samir Z. Zard

Beilstein J. Org. Chem. 2013, 9, 557–576, doi:10.3762/bjoc.9.61

• -arylpiperidines. This strategy is illuminated by the synthetic outline in Scheme 24, where the intermediate radical 124 arising from addition to alkene 123 undergoes a 1,2-aryl shift via cyclopropane 125, a process made irreversible by elimination of a methylsulfonyl radical to give ester 126 [52]. Two new C–C

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

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

trans-2-(2,5-Dimethoxy-4-iodophenyl)cyclopropylamine and trans-2-(2,5-dimethoxy-4-bromophenyl)cyclopropylamine as potent agonists for the 5-HT₂ receptor family

• Adam Pigott,
• Stewart Frescas,
• John D. McCorvy,
• Xi-Ping Huang,
• Bryan L. Roth and
• David E. Nichols

Beilstein J. Org. Chem. 2012, 8, 1705–1709, doi:10.3762/bjoc.8.194

• successful in leading to compounds with high affinity at the 5-HT2 family of receptors; and the more potent stereoisomer of the cyclopropane analogues had the expected (−)-(1R,2S)-configuration. Screening for affinity at various serotonin receptor subtypes, however, revealed that the cyclopropane congeners

• properties which are identical, or at least very similar to those of 1a. We had previously characterized the cyclopropane analogue of a hallucinogenic amphetamine known as DOM (2) and had shown that 3 (DMCPA) had high potency both in vitro and in vivo [1][2][3]. We thus considered whether the cyclopropane

• analogues 4 and 5 might be useful research tools. Accordingly, this report details the synthesis of racemic trans-1-(2,5-dimethoxy-4-iodophenyl)-2-aminocyclopropane (4) and its bromo homolog 5, the resolution of 4 into its (−)-(1R,2S)-enantiomer, as well as the resolution of the cyclopropane carboxylic acid

Influence of cyclodextrin on the solubility of a classically prepared 2-vinylcyclopropane macromonomer in aqueous solution

• Helmut Ritter,
• Jia Cheng and
• Monir Tabatabai

Beilstein J. Org. Chem. 2012, 8, 1528–1535, doi:10.3762/bjoc.8.173

• , assignable to the CH of the cyclopropane ring and of the vinyl group, respectively. The FTIR spectrum shows the typical absorption band of ester groups at 1726 cm−1 and the disappearance of the band of primary amino groups; this also proves the successful condensation between 3 and 4. Due to the faintly

• –2930 (ν CH aliphatic), 1726 (ν C=O of ester), 1639 (ν C=O, amide I), 1545 (δ NH, amide II); 1H NMR (acetone-d6, 300 MHz) δ (ppm) 7.13 (NH), 5.19–4.98 (CH2=CH), 4.11 (COOCH2), 3.85 (CHNH), 2.99 (CH of cyclopropane), 2.82 (CH2NH2), 2.68 (CH2CH2S), 2.47 (CHCO), 2.10 (SCH2CH), 1.61–1.48 (CH2 of

• cyclopropane), 1.40–1.01 (CH2, CH3). Oligomerization of macromonomer 5 to 6 A solution of 5 (0.7 g) in anhydrous DMF (50 mL) was deaerated with nitrogen bubbling for 1 h. Subsequently, a solution of AIBN (0.42 mg, 2.56 µmol) in anhydrous DMF (0.5 mL) was added. The polymerization was carried out at 65 °C for

Synthesis of a novel chemotype via sequential metal-catalyzed cycloisomerizations

• Bo Leng,
• Stephanie Chichetti,
• Shun Su,
• Aaron B. Beeler and
• John A. Porco Jr.

Beilstein J. Org. Chem. 2012, 8, 1338–1343, doi:10.3762/bjoc.8.153

• diversity; cycloisomerization; cyclopropane; diyne; isochromene; π-acid; Introduction Our laboratory has an ongoing interest in discovering transformations that afford novel chemotypes [1][2][3][4]. To this end, we have developed a reaction screening paradigm that enables the discovery of new reaction

• novel polycyclic cyclopropane chemotype. Results and Discussion In an effort to further explore the utility of alkynyl o-benzaldehydes as scaffolds for reaction screening, we designed a focused reaction screen with diynyl benzaldehyde [7] substrate 3. Based on the cycloisomerization/addition reactions

• toluene [16][17]. The reaction afforded polycyclic cyclopropane 6 in good yield (65%) as a single diastereomer (Scheme 2a). Interestingly, reaction of 3 in the presence of only PtCl2 afforded exclusively isochromene 5 in low yield. Further studies revealed that a multicatalytic reaction system [18

Chemistry of polyhalogenated nitrobutadienes, 10: Synthesis of highly functionalized heterocycles with a rigid 6-amino-3-azabicyclo[3.1.0]hexane moiety

• Viktor A. Zapol’skii,
• Jan C. Namyslo,
• Armin de Meijere and
• Dieter E. Kaufmann

Beilstein J. Org. Chem. 2012, 8, 621–628, doi:10.3762/bjoc.8.69

• , they are attached to isochronous carbon atoms at 59.0 ppm. Furthermore, the proton of the NCH fragment (13C NMR: δ = 47.3 ppm) of the cyclopropane ring appears as a triplet at 1.54 ppm (J = 2.3 Hz). Interestingly, the chemical shift of both of the bridgehead protons is 1.35 ppm (dd, J = 4.2, 2.3 Hz

Branching out at C-2 of septanosides. Synthesis of 2-deoxy-2-C-alkyl/aryl septanosides from a bromo-oxepine

• Supriya Dey and
• Narayanaswamy Jayaraman

Beilstein J. Org. Chem. 2012, 8, 522–527, doi:10.3762/bjoc.8.59

• common bromo-oxepine intermediate, involving C–C bond forming organometallic reactions. Unsaturated, seven-membered septanoside vinyl bromides or bromo-oxepines, obtained through a ring expansion methodology of the cyclopropane derivatives of oxyglycals, displayed a good reactivity towards several

Carbamate derivatives and sesquiterpenoids from the South China Sea gorgonian Melitodes squamata

• Li-Si Huang,
• Fei He,
• Hui Huang,
• Xiao-Yong Zhang and
• Shu-Hua Qi

Beilstein J. Org. Chem. 2012, 8, 170–176, doi:10.3762/bjoc.8.18

• well with those previously assigned to the corresponding methyl groups in 8, 9 and other analogues [7][8][9][10][11], which suggests the cis-orientation of the cyclopropane ring [7][8]. The coupling constants (J = 10.0 Hz) between H-5 and H-1/H-6 indicate the trans-relationship of H-5 with H-1 and H-6

Fluorescent hexaaryl- and hexa-heteroaryl[3]radialenes: Synthesis, structures, and properties

• Antonio Avellaneda,
• Courtney A. Hollis,
• Xin He and
• Christopher J. Sumby

Beilstein J. Org. Chem. 2012, 8, 71–80, doi:10.3762/bjoc.8.7

• calculations that show intramolecular charge transfer character in the lowest excited states for hexaaryl[3]radialene derivatives [42]. In the excited state, rotation about the exocyclic bonds of the cyclopropane ring is also possible. The fluorescence emission of the hexaaryl[3]radialenes, coupled with the

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

• substituent, a beta-methoxy eneone system, and a pyrrolinone ring [41]. The incorporation of the chlorovinylidene group was partially elucidated and predicted to be highly similar to the cyclopropane ring formation of curacin A biosynthesis (Figure 6B) ([42], see below). The enzyme cassette comprises a PKS

• ) Formation of the trichloroleucyl starter unit of barbamide (7) synthesis through the non-heme iron(II)-dependent halogenases BarB1 and BarB2. B) Formation of cyclopropane and vinyl chloride functional groups in curacin A (9) and jamaicamide A (8) biosynthesis, respectively. The halogenated carbon is

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

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

• to those previously proposed by Gagosz, evolves through a cyclopropane fragmentation and protodeauration to afford the products 48 in good yields and excellent stereoselectivities. Based on these and other reports demonstrating the ability of gold(I) and platinum(II) catalysts to induce reactions of

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

• rearrangement followed by nucleophilic attack of the Boc-protected nitrogen atom. A similar method to synthesize the 2-vinylpiperidin-3-ol 158 by a highly stereoselective gold-catalyzed allene cyclization has been reported (Scheme 27) [72]. The ring expansion of cyclopropane derivatives provides a powerful

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

• was gathered which proved the reversible nature of the [3,3]-rearrangement in these cyclopropane probes. However, these transformations proved to be stereospecific in nature through gold-stabilized non-classical carbocations 100 and 100', even if the stereochemical information transfer to the product

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

• intermediate. Thus, when 3-methyl-3-nonylcyclopropene (8) was treated with a catalytic amount of [(Ph3P)AuNTf2] in the presence of excess styrene, the alkenyl cyclopropane 44, resulting from intermolecular cyclopropanation triggered by the gold carbene 43, was isolated in 72% yield as a 6:1 mixture of cis

• present. Although no cyclopropane derivative was obtained from this reaction, this transformation has been included in this section because one of the possible mechanisms involves an initial cyclopropanation of the less hindered olefin in 2-methylfuran by the organogold intermediate 51, followed by ring

Gold-catalyzed regioselective oxidation of terminal allenes: formation of α-methanesulfonyloxy methyl ketones

• Yingdong Luo,
• Guozhu Zhang,
• Erik S. Hwang,
• Thomas A. Wilcoxon and
• Liming Zhang

Beilstein J. Org. Chem. 2011, 7, 596–600, doi:10.3762/bjoc.7.69

• of note that α-methanesulfonyloxy ketones are versatile synthetic intermediates that can undergo various reactions [27], including substitution [28], elimination [29], the formation of zinc homoenolates [30], the formation of cyclopropane rings under photo-irradiation [31][32][33], the formation of

The arene–alkene photocycloaddition

• Ursula Streit and
• Christian G. Bochet

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

• has been reported to produce very high yields; however, the lack of regioselectivity in the biradical cyclopropane formation gives the two regioisomers in a ratio of 8:5. Intramolecular reactions The first intramolecular meta photocycloaddition was reported in 1969 by Morrison and Ferree [39]. The

• can be changed [45]. The linear and angular isomer names are derived from the opening of the cyclopropane ring to afford linearly and angularly fused triquinanes. Asymmetric meta photocycloadditions The meta photocycloaddition has the potential to convert planar (thus achiral) molecules into three

• the formation of the cyclopropane ring, and both regioisomers are obtained. A similar approach has been published by Morales et al. who observed diastereoselectivity by the introduction of a chiral center α to the aromatic moiety on the tether [49]. Some diastereoselective approaches where the chiral

Molecular rearrangements of superelectrophiles

• Douglas A. Klumpp

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

• cyclopropane 55. Subsequent deprotonation and hydride abstractions steps give the final product 52. A similar series of reactions affords the isomeric product 53. An interesting rearrangement and cyclization of an acyl dication has been reported [25]. Ionization of the acid chloride 57 in superacid (FSO3H-SbF5