Further exploration of the heterocyclic diversity accessible from the allylation chemistry of indigo

• Alireza Shakoori,
• John B. Bremner,
• Mohammed K. Abdel-Hamid,
• Anthony C. Willis,
• Rachada Haritakun and
• Paul A. Keller

Beilstein J. Org. Chem. 2015, 11, 481–492, doi:10.3762/bjoc.11.54

• ' reagent. This is not unexpected as there are reports of ruthenium-based species catalysing Claisen rearrangements [7] including a similar RCM–Claisen sequence in 2,2'-bis(allyloxy)-1,1'-binaphthyls and O,O'-(but-2-en-1,4-diyl) binaphthols [12][13]. Additionally, examples of C2 to C3 Claisen rearrangement

An unusually stable chlorophosphite: What makes BIFOP–Cl so robust against hydrolysis?

• Roberto Blanco Trillo,
• Jörg M. Neudörfl and
• Bernd Goldfuss

Beilstein J. Org. Chem. 2015, 11, 313–322, doi:10.3762/bjoc.11.36

• , in Pd catalysts. Keywords: chirality; hydrolysis; phosphorus; rearrangements; terpenoids; Introduction Phosphorus halides are highly reactive intermediates for the synthesis of phosphites and phosphoramidites [1][2][3][4][5], which are widely used, for example, as ligands in catalysts [6][7][8][9

Anionic sigmatropic-electrocyclic-Chugaev cascades: accessing 12-aryl-5-(methylthiocarbonylthio)tetracenes and a related anthra[2,3-b]thiophene

• Laurence Burroughs,
• John Ritchie,
• Mkhethwa Ngwenya,
• Dilfaraz Khan,
• William Lewis and
• Simon Woodward

Beilstein J. Org. Chem. 2015, 11, 273–279, doi:10.3762/bjoc.11.31

• via nominal [3,3]-sigmatropic rearrangements of xanthates. As the thiocarbamate products derived from these are predicted to be easily hydrolised to thiolates this potentially offers a simple route to a protected SH analogue of 3. Lin’s chemistry [14] cannot be used as no simple method to modify SOPh

• to SH is available. We proposed that use of starting material xanthate 1c should provide suitably protected 5-thiotetracene derivatives directly (Scheme 2). The required [3,3]-sigmatropic rearrangements and subsequent 6π elecrocyclisations of 1c have precise stereochemical requirements (Scheme 2

• , the possibility of aromatisation of 6 through Chugaev [22] syn elimination. Finally the system of Scheme 2 provides a unique opportunity to probe if these rearrangements do indeed proceed from the neutral xanthates 1c or via the previously unprecedented 1d–2d–6d anionic cascades. Results and

Anomalous diffusion of Ibuprofen in cyclodextrin nanosponge hydrogels: an HRMAS NMR study

• Monica Ferro,
• Franca Castiglione,
• Carlo Punta,
• Lucio Melone,
• Walter Panzeri,
• Barbara Rossi,
• Francesco Trotta and
• Andrea Mele

Beilstein J. Org. Chem. 2014, 10, 2715–2723, doi:10.3762/bjoc.10.286

• structure of the CDNSEDTA 1:8 is expected to show a high degree of heterogeneity in the distribution of pores, due to rearrangements caused by the steric hindrance. The TEM image of Figure 4b shows the details of the pores heterogeneity and the sponge-like morphology. The slightly superdiffusive behaviour

Photorelease of phosphates: Mild methods for protecting phosphate derivatives

• Sanjeewa N. Senadheera,
• Abraham L. Yousef and
• Richard S. Givens

Beilstein J. Org. Chem. 2014, 10, 2038–2054, doi:10.3762/bjoc.10.212

• modest efficiency, Φ = 0.028. Similarly, the methoxy analog, 1,4-MNA DEP (14b), released DEP, but with a much lower efficiency (Φ = 0.0078). Both quantitatively produced DEP and, pleasingly, underwent photo-Favorskii rearrangements converting the aryl ketones to methyl naphthylacetates, blue-shifting the

• byproduct chromophore absorptions. Both 14a and 14b now become the first new examples of photo-Favorskii rearrangements, here on a naphthyl platform. Previous examples are limited to phenacyl frameworks [6][7][8][9][15][38][39]. It is interesting to note, however, that replacement of the OH with OMe in the

• cyclization to form the ‘Favorskii intermediate’ 33 [6][8][15][26][38][39][48]. In contrast to the 1,4-naphthyl design, neither 10 nor 24 underwent Favorskii rearrangements. While both gave stoichiometric release of DEP, the chromophores either remain intact (for 10) as also reported for other 2

Synthesis of 2-substituted tryptophans via a C3- to C2-alkyl migration

• Michele Mari,
• Simone Lucarini,
• Francesca Bartoccini,
• Giovanni Piersanti and
• Gilberto Spadoni

Beilstein J. Org. Chem. 2014, 10, 1991–1998, doi:10.3762/bjoc.10.207

• the corresponding pyrrolindoline derivative without any trace of the rearranged 2-substituted tryptophan, even with extended reaction times. The electronic properties of the migratory group have a pronounced effect on the reaction profile. As known from other Wagner–Meerwein-type rearrangements [71

Application of cyclic phosphonamide reagents in the total synthesis of natural products and biologically active molecules

• Thilo Focken and
• Stephen Hanessian

Beilstein J. Org. Chem. 2014, 10, 1848–1877, doi:10.3762/bjoc.10.195

• products or bioactive molecules will be discussed [10]. Similar technologies to the ones discussed here without such applications and other uses of chiral phosphonamide reagents in asymmetric synthesis such as Denmark’s carbanion-accelerated Claisen rearrangements [11][12] have been reviewed elsewhere [13

cis–trans Isomerization of silybins A and B

• Michaela Novotná,
• Radek Gažák,
• David Biedermann,
• Florent Di Meo,
• Petr Marhol,
• Marek Kuzma,
• Lucie Bednárová,
• Kateřina Fuksová,
• Patrick Trouillas and
• Vladimír Křen

Beilstein J. Org. Chem. 2014, 10, 1047–1063, doi:10.3762/bjoc.10.105

• (compared to O-9) by 4 kcal·mol−1. The coordination with boron initiates isomerization at C-2, C-3 and C-10, C-11 by charge rearrangements (e.g., proton release and formation of IIb in Scheme 5). The mechanisms related to both sites can be considered separately, as both moieties are electronically

• BF3 complexation as confirmed by the complexation energies (Table 3). Following complexation, the D-ring opening proceeds (Scheme 6), allowing molecular rearrangements and isomerization after ring closure. The observation of the isomerization of 1 (or 2) at C-11 that occurs in EtOAc but not in DMF can

Dimerisation, rhodium complex formation and rearrangements of N-heterocyclic carbenes of indazoles

• Zong Guan,
• Jan C. Namyslo,
• Martin H. H. Drafz,
• Martin Nieger and
• Andreas Schmidt

Beilstein J. Org. Chem. 2014, 10, 832–840, doi:10.3762/bjoc.10.79

• -ylidene with acetylenes. Indazol-3-ylidenes which possess an aryl ring at N1 rearrange to give substituted acridines by a ring-cleavage/pericyclic ring-closure reaction sequence (2→A→B→11) (Scheme 3). It proved to be advantageous to start these rearrangements from indazolium salts which are readily

• available by copper-catalyzed aryl couplings or Buchwald–Hartwig reactions [22]. Pyrazol-3-ylidenes rearrange similarly to quinolines [17]. We report here on two unexpected rearrangements of indazol-3-ylidene, and trapping reactions of the N-heterocyclic carbene with rhodium. Results and Discussion On

• : C51H42N2OP2Rh calcd for 863.1827; found: 863.1827. General procedure for the rearrangements of the indazole carbene dimers to 16 A solution of 1.0 mmol of the dimers of the indazole carbenes 13a/13b/13d in 20 mL of xylene was stirred at reflux temperature for 3 hours. After the solvent was distilled off in

The Flögel-three-component reaction with dicarboxylic acids – an approach to bis(β-alkoxy-β-ketoenamides) for the synthesis of complex pyridine and pyrimidine derivatives

• Mrinal K. Bera,
• Moisés Domínguez,
• Paul Hommes and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2014, 10, 394–404, doi:10.3762/bjoc.10.37

• β-ketoenamides 14 and 20 with hydroxylamine hydrochloride to pyridine-N-oxides 28 and 30 and their subsequent Boekelheide rearrangements furnishing functionalized bis(pyrimidine) derivative 29 and pyrimidine/pyridine conjugate 31. Riley oxidation of bis(pyrimidine) derivative 23a and conversion of

Synthesis of new enantiopure poly(hydroxy)aminooxepanes as building blocks for multivalent carbohydrate mimetics

• Léa Bouché,
• Maja Kandziora and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2014, 10, 213–223, doi:10.3762/bjoc.10.17

• ; 1,2-oxazines; rearrangements; reductions; Introduction Since carbohydrates play a crucial role in biochemistry, compounds mimicking their structure and/or function (carbohydrate mimetics) have attracted great attention in academic research and in drug development [1][2][3]. These mimetics should not

• coordination of the lithium cation to the nitrone oxygen is possible. The Lewis acid-induced rearrangements of 1,2-oxazines syn-7, syn-9 and syn-10 were achieved in moderate to good yields using TMSOTf as promoter (Scheme 4). A higher yield of 73% was achieved for the p-bromophenyl derivative 13 (isolated as a

Synthesis of the B-seco limonoid core scaffold

• Hanna Bruss,
• Hannah Schuster,
• Rémi Martinez,
• Markus Kaiser,
• Andrey P. Antonchick and
• Herbert Waldmann

Beilstein J. Org. Chem. 2014, 10, 194–208, doi:10.3762/bjoc.10.15

• , entry 1). Intermediary, the silyl enol ether and the silyl ketene acetal are formed. However, after the rearrangement, the keto-functionality can be set free again during an acidic work-up. In terms of yield and diastereoselectivity there was no difference observed between rearrangements with

• rearrangements of the model substrates with an undecorated A ring, we attempted to access the B-seco limonoid scaffold by an analogous rearrangement of bicyclic precursor 66 (Scheme 8). The elaboration of the required bicyclic system commenced with enone 15 (Scheme 8). Initially, we envisaged an α-vinylation via

• rigid than the bicyclic system 66 and therefore, in analogy to the results of the rearrangements with the model substrates, probably preferably rearrange via a pseudo-axial attack. The open-chain precursor 70 was obtained by MOM protection of diol 64, selective cleavage of the primary TBS group and

Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

• Alexander O. Terent'ev,
• Dmitry A. Borisov,
• Vera A. Vil’ and
• Valery M. Dembitsky

Beilstein J. Org. Chem. 2014, 10, 34–114, doi:10.3762/bjoc.10.6

• performing the Curtius and Wolff rearrangements to form 1,2-dioxolane ring-retaining products was exemplified by the synthesis of ethyl (3,5,5-trimethyl-1,2-dioxolan-3-yl)methylcarbamate (152) and methyl 3-(3,5,5-trimethyl-1,2-dioxolan-3-yl)propanoate (154) (through formation of stable diazodioxolane 153

• Kobayashi cyclization of hydroperoxides, the reaction of 1,4-diketones with hydrogen peroxide, the intramolecular nucleophilic substitution by the hydroperoxide group, the cyclization with participation of halogenonium ion donors, acid-mediated rearrangements of peroxides, the palladium-catalyzed

[²H₂₆]-1-epi-Cubenol, a completely deuterated natural product from Streptomyces griseus

• Christian A. Citron and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2013, 9, 2841–2845, doi:10.3762/bjoc.9.319

• enzyme catalysis [34], but such approaches may not be suitable for terpenes that are in many cases unstable under acidic conditions or may tend to thermal rearrangements [35]. The successful formation of a completely deuterated natural product (up to 90% 2H) by fermentation has recently been reported for

One-pot sequential synthesis of isocyanates and urea derivatives via a microwave-assisted Staudinger–aza-Wittig reaction

• Diego Carnaroglio,
• Katia Martina,
• Giovanni Palmisano,
• Andrea Penoni,
• Claudia Domini and
• Giancarlo Cravotto

Beilstein J. Org. Chem. 2013, 9, 2378–2386, doi:10.3762/bjoc.9.274

• , Hoffman and Lossen rearrangements have been used quite often in the past and are still used for specific applications [10][11][12][13]. The Staudinger–aza-Wittig reactions have played a pivotal role in the construction of cyclic and acyclic compounds [14][15][16][17][18][19]. The replacement of phosgene

Gold(I)-catalyzed 6-endo hydroxycyclization of 7-substituted-1,6-enynes

• Ana M. Sanjuán,
• Alberto Martínez,
• Patricia García-García,
• Manuel A. Fernández-Rodríguez and
• Roberto Sanz

Beilstein J. Org. Chem. 2013, 9, 2242–2249, doi:10.3762/bjoc.9.263

• external nucleophiles undergo skeletal rearrangements to afford products such as III (single cleavage) [14]. However, reactions of II with alcohols or water give the corresponding products of alkoxy(hydroxy)cyclization IV [15][16][17] (Scheme 1). The less common 6-endo cyclization via metal carbenes V was

Sequential Diels–Alder/[3,3]-sigmatropic rearrangement reactions of β-nitrostyrene with 3-methyl-1,3-pentadiene

• Peter A. Wade,
• Alma Pipic,
• Matthias Zeller and
• Panagiota Tsetsakos

Beilstein J. Org. Chem. 2013, 9, 2137–2146, doi:10.3762/bjoc.9.251

• 3 to 19 by [3,3]-sigmatropic rearrangements (vide infra). Sn(IV)-catalyzed reactions of nitronic esters The possibility that ternary adduct 12a,b could arise from ring opening of one of the nitronic esters was considered. Neither nitronic ester 4 nor 7 afforded 12a,b when treated with tin(IV

• and no other significant steric interactions are apparent for the transition state. Other rearrangements to give products where the nitro and phenyl groups are trans (nitro compounds 18 and previously studied 22a) [1] were successful. Even nitronic ester 26a affords the bicyclo[2.2.2]alkene 28a in 72

Flow synthesis of a versatile fructosamine mimic and quenching studies of a fructose transport probe

• Matthew B. Plutschack,
• D. Tyler McQuade,
• Giulio Valenti and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2013, 9, 2022–2027, doi:10.3762/bjoc.9.238

• NBDM quenching was observed even at sugar concentrations as high as 100 mM. Conclusion In conclusion, we report the flow synthesis of the fluorescent fructose mimic NBDM. While we demonstrated for the first time that resin-supported nitrite ions can facilitate Tiffeneau–Demjanov rearrangements, we

• found that solution phase rearrangements were superior resulting in throughput gains >63-fold relative to batch conditions. We also demonstrated that the output of the Tiffeneau–Demjanov rearrangement reactor could be telescoped into the oxime reactions. The oxime reaction was very efficient exhibiting

Gold-catalyzed reaction of oxabicyclic alkenes with electron-deficient terminal alkynes to produce acrylate derivatives

• Yin-wei Sun,
• Qin Xu and
• Min Shi

Beilstein J. Org. Chem. 2013, 9, 1969–1976, doi:10.3762/bjoc.9.233

• interest in gold-catalyzed C–C [57][58][59][60][61] or C–X bond [62][63][64][65][66][67] formation reactions. So far, we have reported a variety of gold-catalyzed intramolecular rearrangements with highly strained small rings for C–C or C–X bond formations [57][58][59][62][63][64][65][66][67][68]. Based on

Gold-catalyzed regioselective oxidation of propargylic carboxylates: a reliable access to α-carboxy-α,β-unsaturated ketones/aldehydes

• Kegong Ji,
• Jonathan Nelson and
• Liming Zhang

Beilstein J. Org. Chem. 2013, 9, 1925–1930, doi:10.3762/bjoc.9.227

• following observations and considerations: a) propargylic carboxylates of type 4a with an internal C–C triple bond typically undergo facile 3,3-rearrangements [26][27][28][29][30] instead of 1,2-acyloxy migrations. The former process would eventually lead to the formation of the enones 6 [31]. Due to

Gold-catalyzed intermolecular coupling of sulfonylacetylene with allyl ethers: [3,3]- and [1,3]-rearrangements

• Jungho Jun,
• Hyu-Suk Yeom,
• Jun-Hyun An and
• Seunghoon Shin

Beilstein J. Org. Chem. 2013, 9, 1724–1729, doi:10.3762/bjoc.9.198

• organic chemistry, mediating a variety of C–C and C–X (heteroatom) bond formations, various tandem reactions and rearrangements [1]. Despite these significant advances, overcoming entropic penalty in intermolecular coupling of alkenes with alkynes is still a major challenge in gold catalysis, reflected by

• -substituent, the steric nature of R2 and R3 substituents determined the ratio of [3,3]- versus [1,3]-products. Finally, R4 substituent at the allyl group (2n) retarded the transformation severely, indicating an unfavorable steric interaction. Unlike previous intramolecular [3,3]-sigmatropic rearrangements [13

• with a lower amount of the excess reactant. However, it is accompanied by a significant amount of byproduct(s) such as 4 and 5, resulting from the dissociation of the allyl C–O cleavage. While the linear allyl ethers preferred [3,3]-sigmatropic rearrangements, the presence of an α-substituent led to a

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

• titanacyclopentane that subsequently fragments in a stereospecific manner [31]. We were intrigued by the apparent difference in selectivity observed in cyclopropane rearrangements proceeding via a neutral pathway versus those proceeding by more polar or directed mechanisms. Although the E geometry of the central

• a β-ketoester. Retrosynthesis utilizing Rychnovsky’s cyanohydrin acetonide methodology. Nickel-catalyzed reductive coupling of alkynes and epoxides. Potential transition states and stereochemical outcomes for a concerted 1,5-hydrogen rearrangement. Rearrangements of vinylcyclopropanes to acylic 1,4

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

• -promoted ET and PET conditions. Using rearrangements of radicals and ions to distinguish mechanistic pathways for ET-reactions. Reductive ET reactions of the probe I (left) and oxidative ET reactions of probe II (right). Reaction of silyl ether 1a with Cu(OAc)2 in the absence or presence of n-Bu4NF. SmI2

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

• complex [29] at the less-hindered carbon of the epoxide would provide 26. Acid- and Lewis acid promoted Payne rearrangements of epoxy alcohols [33][34] and epoxy methyl ethers [35] have been described, but we are unaware of any prior reports of Payne rearrangements of the bulkier epoxy trityl ethers

3-Pyridylnitrene, 2- and 4-pyrimidinylcarbenes, 3-quinolylnitrenes, and 4-quinazolinylcarbenes. Interconversion, ring expansion to diazacycloheptatetraenes, ring opening to nitrile ylides, and ring contraction to cyanopyrroles and cyanoindoles

• Curt Wentrup,
• Nguyen Mong Lan,
• Adelheid Lukosch,
• Pawel Bednarek and
• David Kvaskoff

Beilstein J. Org. Chem. 2013, 9, 743–753, doi:10.3762/bjoc.9.84

• either the nitrenes or the diazacycloheptatetraenes to nitrile ylides. Keywords: carbene-nitrene interconversion; diazepines; flash vacuum thermolysis; matrix photochemistry; nitrile ylides; reactive intermediates; Introduction A multitude of rearrangements of heterocyclic nitrenes have been described

• 47 → nitrile 48. The data demonstrate that carbene 55 does not convert thermally to nitrene 45. In other words, although carbene–nitrene rearrangements are known to occur [1][19] (see, e.g., Scheme 1 and Scheme 10 above), they may be bypassed when ring opening to nitrile ylides becomes more

• cyanopyrroles by FVT of tetrazolylpyrimidines. Rearrangements of pyrimidinylcarbenes to cyanopyrroles via nitrile ylides 31 and 37. Rearrangements of phenyl(dimethylpyrimidinyl)carbene. Photolysis of 3-azido-2-phenylquinoline. Preparative FVT of 3-azido-2-phenylquinoline. FVT of 2-phenyl-4-quinazolinylcarbene