Thermodynamically stable [4 + 2] cycloadducts of lanthanum-encapsulated endohedral metallofullerenes

• Yuta Takano,
• Yuki Nagashima,
• M. Ángeles Herranz,
• Nazario Martín and
• Takeshi Akasaka

Beilstein J. Org. Chem. 2014, 10, 714–721, doi:10.3762/bjoc.10.65

• of the cycloadducts of EMFs has not been well-studied to date; the investigation of this interconversion serves to demonstrate the existence of a dynamic process in the molecules and is regarded as one index of the bonding energy of the addition position of the fullerene and the addend. Among various

• slow or fast to allow their observation in an NMR time scale. The signals from the AB-quartet of 4a coalesce at 290 K (= Tc) indicate a dynamic process, which is attributed to the boat-to-boat interconversion of the cyclohexane ring of the addend similarly to the related carbocyclic analogues of C60

Chromatographically separable rotamers of an unhindered amide

• Mario Geffe,
• Lars Andernach,
• Oliver Trapp and
• Till Opatz

Beilstein J. Org. Chem. 2014, 10, 701–706, doi:10.3762/bjoc.10.63

• .10.63 Abstract Surprisingly stable formamide rotamers were encountered in the tetrahydroisoquinoline and morphinan series of alkaloids. We investigated the hindered rotation around the amide bond by dynamic high-performance liquid chromatography (DHPLC) and kinetic measurements of the interconversion of

• the second development immediately followed the air-drying of the plate. If one hour at room temperature lay between the first and the second development, two weak off-diagonal spots indicated that interconversion of both species had taken place to a small extent. When the temperature was increased to

• 75 °C during a 15 min drying period, four spots with roughly equal intensity resulted from the second 2D-TLC run and indicated complete interconversion. A look into the literature revealed that the occurrence of separable amide rotamers of 1-benzyl-N-formyl-1,2,3,4-tetrahydroisoquinolines had been

Recent applications of the divinylcyclopropane–cycloheptadiene rearrangement in organic synthesis

• Sebastian Krüger and
• Tanja Gaich

Beilstein J. Org. Chem. 2014, 10, 163–193, doi:10.3762/bjoc.10.14

• desired DVCPR in almost quantitative yield at elevated temperature, followed by removal of the silyl-protecting group under acidic conditions to furnish cycloheptenone 70. Standard functional group interconversion furnished diolefin 71. Subjection of this compound to Heck coupling conditions resulted in

• 96, for which the yield and enantioselectivity was determined starting from 93. Standard functional group interconversion first provided exo-methylene 97, followed by ruthenium-catalyzed oxidative cleavage of the installed exo-methylene moiety [94] to give tricyclic ketone 98, which can be converted

The difluoromethylene (CF₂) group in aliphatic chains: Synthesis and conformational preference of palmitic acids and nonadecane containing CF₂ groups

• Yi Wang,
• Ricardo Callejo,
• Alexandra M. Z. Slawin and
• David O’Hagan

Beilstein J. Org. Chem. 2014, 10, 18–25, doi:10.3762/bjoc.10.4

• -tetrafluorohexadecanoic acid (6c). The X-ray structure of 8,8,11,11-tetrafluorononadecane (27). Conformational interconversion of 1,4-di-CF2 motif. Synthesis route to 8,8-difluorohexadecanoic acid (6a). The synthesis of palmitic acid analogues 6b and 6c. Synthesis route to the tetrafluorinated alkane 27. Supporting

Plakilactones G and H from a marine sponge. Stereochemical determination of highly flexible systems by quantitative NMR-derived interproton distances combined with quantum mechanical calculations of ¹³C chemical shifts

• Simone Di Micco,
• Angela Zampella,
• Maria Valeria D’Auria,
• Carmen Festa,
• Simona De Marino,
• Raffaele Riccio,
• Craig P. Butts and
• Giuseppe Bifulco

Beilstein J. Org. Chem. 2013, 9, 2940–2949, doi:10.3762/bjoc.9.331

• extend the application of NMR-derived interproton distances to a highly flexible molecular system with simultaneous assignment of four non-contiguous stereocenters. Chemical derivatization and quantum mechanical calculations of 13C on plakilactone G along with a plausible biogenetic interconversion

• consistent with anti-1,2-diol type C. Therefore the 7R,8S configuration is assigned. Notably, considering the plausible biogenetic interconversion of an epoxide and a diol, the above absolute configuration at C-7 and C-8 of plakilactone G is in full agreement with the trans-epoxide 2b. Having assigned the

• probability of 62.9% (Table 5), whereas for 1b–d we found a probability of 1.9%, 5.4% and 29.7% (Table 5), respectively. Isomers 1a and 1d differ only in the configuration at C-4, and considering a putative interconversion between diol 1 and epoxide 2 and a common biogenetic pathway in combination with the

Less reactive dipoles of diazodicarbonyl compounds in reaction with cycloaliphatic thioketones – First evidence for the 1,3-oxathiole–thiocarbonyl ylide interconversion

• Valerij A. Nikolaev,
• Alexey V. Ivanov,
• Ludmila L. Rodina and
• Grzegorz Mlostoń

Beilstein J. Org. Chem. 2013, 9, 2751–2761, doi:10.3762/bjoc.9.309

• temperature dependence of the main reaction product type obtained from dimethyl diazomalonate and 2,2,4,4-tetramethyl-3-thioxocyclobutanе-1-one as well as to verify reversibility of the thiocarbonyl ylide and 1,3-oxathiole interconversion, the calculations of the energy profile for the transformation of 1,3

• . Thus, the observed process is the first example of a reversible interconversion of a 1,3-oxathiole into the corresponding thiirane via the corresponding thiocarbonyl ylide. Subsequently formed thiirane easily undergoes desulfurization, and finally the respective alkene is formed as an isolable compound

• interconversion and to explain the observed dependence in the formation of the main reaction product type from the temperature, the computations were performed at the DFT PBE1PBE/6-31G(d) level of the energy profile for the transformation of 1,3-oxathiole 3e to alkene 5e (Figure 3, Supporting Information File 1

Biosynthesis of rare hexoses using microorganisms and related enzymes

• Zijie Li,
• Yahui Gao,
• Hideki Nakanishi,
• Xiaodong Gao and
• Li Cai

Beilstein J. Org. Chem. 2013, 9, 2434–2445, doi:10.3762/bjoc.9.281

• extensively studied, particularly from D-galactose by L-arabinose isomerase (AI, EC 5.3.1.4) (Scheme 1) [14][15][16][17][18][19][20]. As the interconversion equilibrium between D-galactose and D-tagatose shifts toward D-tagatose at higher temperatures, biocatalysts with greater thermal stability are preferred

• residues in the active site, the metal coordinating site and the substrate-binding site of these enzymes (Figure 1) [37][38]. After all, the interconversion between D-fructose and D-psicose catalyzed by DTEase enzymes is an equilibrium process, thus large scale and high yield production of D-psicose as

• -phosphate isomerase from Lactococcus lactis [74] catalyze two reversible isomerization reactions (interconversion between D-psicose and D-allose vs interconversion between D-psicose and D-altrose) with D-altrose as a byproduct. In contrast, L-rhamnose isomerase from Bacillus pallidus [75] and ribose-5

An overview of the synthetic routes to the best selling drugs containing 6-membered heterocycles

• Marcus Baumann and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2013, 9, 2265–2319, doi:10.3762/bjoc.9.265

• protonation steps. This is followed by Boc-protection and interconversion of the ethyl ester to its amide derivative 2.82 in 80% overall yield for this telescoped process. The primary amide in 2.82 was then oxidised via a modern variant of the classical Hoffmann rearrangement using phenyliodine diacetate

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

• intermediate. The initially isolated nitronic ester cycloadducts underwent tin(IV)-catalyzed interconversion, presumably via zwitterion intermediates. Cycloadducts derived from the reaction at the less substituted double bond of (E)-3-methyl-1,3-pentadiene underwent a [3,3]-sigmatropic rearrangement on heating

• nitronic ester 7 or formation of nitronic ester 4, presumably depending on relative thermodynamic stabilities of the two nitronic esters. Thus, it is thought that nitronic ester 4 is at least 2 kcal/mol more stable than nitronic ester 7. Interconversion of nitronic esters 5 and 6 is thought to occur via

• )-catalyzed [3,3]-sigmatropic rearrangement of nitronic ester 5 affords nitro compound 16 (vide infra). The rapid interconversion of nitronic esters 2 and 3 likely reflects the greater ease of rotation for the cyclo zwitterion 17. Here bond breaking and reformation is at a secondary rather than tertiary

An investigation of the observed, but counter-intuitive, stereoselectivity noted during chiral amine synthesis via N-chiral-ketimines

• Thomas C. Nugent,
• Richard Vaughan Williams,
• Andrei Dragan,
• Alejandro Alvarado Méndez and
• Andrei V. Iosub

Beilstein J. Org. Chem. 2013, 9, 2103–2112, doi:10.3762/bjoc.9.247

• , these researchers refer back to an earlier body of literature that focused on cis/trans-imine interconversion in protic solvents or at high temperature [55][56][57]. A directly relevant study by Boyd et al. [55] convincingly established that protic solvents allow PEA imine isomerization, while aprotic

Structures of the reaction products of the AZADO radical with TCNQF₄ or thiourea

• Hideto Suzuki,
• Yuta Kawahara,
• Hiroki Akutsu,
• Jun-ichi Yamada and
• Shin’ichi Nakatsuji

Beilstein J. Org. Chem. 2013, 9, 1487–1491, doi:10.3762/bjoc.9.169

• usually seen in other thiourea-derived complexes [13]. It is anticipated from the X-ray data at room temperature that AZADO molecules within the thiourea channels are disordered and it appears to be due to dynamic interconversion between the six orientations with essentially equal occupancies of the

True and masked three-coordinate T-shaped platinum(II) intermediates

• Manuel A. Ortuño,
• Salvador Conejero and
• Agustí Lledós

Beilstein J. Org. Chem. 2013, 9, 1352–1382, doi:10.3762/bjoc.9.153

• bending energy profile maintains the same basic features: the T-shaped configurations of the 14-electron species are energy minima, and their cis-like to trans-like interconversion occurs via transition states with Y-shaped configurations [2]. The X-ray structure of the recently reported three-coordinate

Establishing the concept of aza-[3 + 3] annulations using enones as a key expansion of this unified strategy in alkaloid synthesis

• Aleksey I. Gerasyuto,
• Zhi-Xiong Ma,
• Grant S. Buchanan and
• Richard P. Hsung

Beilstein J. Org. Chem. 2013, 9, 1170–1178, doi:10.3762/bjoc.9.131

• -isopropeleine interconversion. Retrosynthesis of propyleine (12). Synthesis of allyl alcohol 25. Catalyst screening and optimization. Synthesis of the annulation precursor 17. Aza-[3 + 3] annulations of 17-cis. Supporting Information Supporting Information File 110: Experimental section. Acknowledgements

Use of 3-[¹⁸F]fluoropropanesulfonyl chloride as a prosthetic agent for the radiolabelling of amines: Investigation of precursor molecules, labelling conditions and enzymatic stability of the corresponding sulfonamides

• Reik Löser,
• Steffen Fischer,
• Achim Hiller,
• Martin Köckerling,
• Uta Funke,
• Aurélie Maisonial,
• Peter Brust and
• Jörg Steinbach

Beilstein J. Org. Chem. 2013, 9, 1002–1011, doi:10.3762/bjoc.9.115

• electrophilic agents can be exchanged by reaction with fluoride even in the presence of water to form the corresponding sulfonyl fluorides [21]. Hence, the sulfonyl chloride has to be generated by interconversion of a different, less reactive sulfur-containing functional group after radiofluorination. Sulfonyl

• transformation of the thiocyano group of 9 to the chlorosulfonyl group leading to 3-fluoropropanesulfonyl chloride (10). This functional group interconversion using aqueous chlorine has been known for a long time [27] but has received little attention in synthetic organic chemistry. Following this approach

Appel-reagent-mediated transformation of glycosyl hemiacetal derivatives into thioglycosides and glycosyl thiols

• Tamashree Ghosh,
• Abhishek Santra and
• Anup Kumar Misra

Beilstein J. Org. Chem. 2013, 9, 974–982, doi:10.3762/bjoc.9.112

• the gated 1H coupled 13C NMR spectra of compounds 32 and 33 confirmed the exclusive formation of β-products [47][48]. It is presumed that the reaction of the glycosyl hemiacetal derivative with the combination of CBr4 and PPh3 furnished α-glycosyl bromide in the first step. Interconversion of the α

4-Pyridylnitrene and 2-pyrazinylcarbene

• Curt Wentrup,
• Ales Reisinger and
• David Kvaskoff

Beilstein J. Org. Chem. 2013, 9, 754–760, doi:10.3762/bjoc.9.85

• -diazacyclohepta-1,2,4,6-tetraene (20). Further photolysis causes ring opening to the ketenimine 27. Keywords: carbene–nitrene interconversion; diazepines; flash vacuum thermolysis; matrix photochemistry; nitrile ylides; reactive intermediates; Introduction The carbene–nitrene interconversion exemplified with

• contraction is highly exothermic, the product will be chemically activated [14], and therefore interconversion of the two cyanopyrroles cannot be avoided. Only a minute trace of 4,4’-azopyridine is formed under these conditions. The total yield of the cyanopyrroles is low because of heavy charring inside the

• pyrolysis tube. The exact mechanisms of ring contraction in arylnitrenes are under investigation, but in the case of 2-pyridylnitrene (Scheme 2) three routes to the cyanopyrroles have been described [10], as has their thermal interconversion [9][10]. The analogous, concerted ring contraction of

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

• drop to 1.2:1 due to the thermal interconversion of 7 and 8 [10][20]. The reaction mechanism was probed by calculations at the B3LYP/6-31G* level, which has been found to be adequate for other, similar reactions [11][13][17][21]. The transition state for the ring opening of the cyclic ketenimine 16 to

• strongly exothermic reactions. Consequently, when the reaction is performed in the low-pressure gas phase, the reaction products carry excess thermal (rovibrational) energy, which facilitates the sigmatropic shifts of H, CN, and CH3, which will cause interconversion of the cyanopyrroles [28]. In many cases

Complete σ* intramolecular aromatic hydroxylation mechanism through O₂ activation by a Schiff base macrocyclic dicopper(I) complex

• Albert Poater and
• Miquel Solà

Beilstein J. Org. Chem. 2013, 9, 585–593, doi:10.3762/bjoc.9.63

• topic is still to unravel, either experimentally or by calculations, which of the side-on μ-η2:η2-peroxo and bis(μ-oxo) isomeric Cu2O22+ cores are present, and in the case that they exist, to study the feasibility of their interconversion [15][16][17][18][19], tuning either the metallic complex or the

Inter- and intramolecular enantioselective carbolithiation reactions

• Asier Gómez-SanJuan,
• Nuria Sotomayor and
• Esther Lete

Beilstein J. Org. Chem. 2013, 9, 313–322, doi:10.3762/bjoc.9.36

• . These secondary α-carbamoyloxybenzyllithiums are configurationally stable and can be trapped. The authors assume that the problem of these enantioselective carbolithiations is due to the interconversion of the conformers, formed by coordination of n-BuLi and the chiral ligand, being too slow, and that

Radical zinc-atom-transfer-based carbozincation of haloalkynes with dialkylzincs

• Fabrice Chemla,
• Florian Dulong,
• Franck Ferreira and
• Alejandro Pérez-Luna

Beilstein J. Org. Chem. 2013, 9, 236–245, doi:10.3762/bjoc.9.28

• -bromovinyl radical 15 of E geometry. Substitution by electron-withdrawing groups slows down E to Z isomerization of vinylic radicals, and therefore, due to the presence of the bromine atom, interconversion of (E)-15 into (Z)-15 should not be fast. Thus, (E)-15 reacts by Zn atom transfer prior to its

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

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

• reaction of the conjugated bisallenes. As a matter of fact, these studies also demonstrate that 2 is the most likely intermediate in the thermal interconversion of 1,5-hexadiyne (129) to 130, a Cope-type rearrangement that was discovered and discussed thoroughly by Huntsman and co-workers [108][109][110

Design and synthesis of quasi-diastereomeric molecules with unchanging central, regenerating axial and switchable helical chirality via cleavage and formation of Ni(II)–O and Ni(II)–N coordination bonds

• Vadim A. Soloshonok,
• José Luis Aceña,
• Hisanori Ueki and
• Jianlin Han

Beilstein J. Org. Chem. 2012, 8, 1920–1928, doi:10.3762/bjoc.8.223

• chelating ring resulting in a screw sense of helical chirality. The transcoordination motion in these complexes is expected to be controlled in a way that noncoordinated sites, i.e., E in 5 and A in 6, will move up and down, respectively, resulting in the interconversion of complexes 5 and 6. This assumed

• . Initial assignment of the structures of compounds 19/20 by NMR was not possible because of the very fast exchange between Ni–O=C and Ni–NH=C chelation. Thus, due to fast interconversion between compounds 19 and 20, only broad signals were observed in the 1H NMR spectra recorded at ambient temperature

Determination of the relative configuration of tropinone and granatanone aldols by using TBDMS ethers

• Ryszard Lazny,
• Aneta Nodzewska,
• Katarzyna Sidorowicz and
• Przemyslaw Kalicki

Beilstein J. Org. Chem. 2012, 8, 1877–1883, doi:10.3762/bjoc.8.216

• relative configurations of tert-butyldimethylsilyl (TBDMS) ethers of all four diastereomers of the aldols of tropinone (8-methyl-8-azabicyclo[3.2.1]octan-3-one), as well as of granatanone (9-methyl-9-azabicyclo[3.3.1]nonan-3-one), were determined from NMR data, and from the observed interconversion of the

Synthesis of conformationally restricted glutamate and glutamine derivatives from carbonylation of orthopalladated phenylglycine derivatives

• Esteban P. Urriolabeitia,
• Eduardo Laga and
• Carlos Cativiela

Beilstein J. Org. Chem. 2012, 8, 1569–1575, doi:10.3762/bjoc.8.179

• interconversion between the two possible diastereoisomers (RR/SS and RS/SR) through cleavage of the chloride bridges, as well as the potential formation of cisoid and transoid geometric isomers. The breakage of the chloride bridging system by NC5D5 and "in situ" formation of the corresponding mononuclear

Synthesis and evaluation of new guanidine-thiourea organocatalyst for the nitro-Michael reaction: Theoretical studies on mechanism and enantioselectivity

• Tatyana E. Shubina,
• Matthias Freund,
• Sebastian Schenker,
• Timothy Clark and
• Svetlana B. Tsogoeva

Beilstein J. Org. Chem. 2012, 8, 1485–1498, doi:10.3762/bjoc.8.168

• −1, Table 3). Thus, in the case of the 7-TABD catalyst, interconversion between the initial complexes is less probable. Again, as in the case of catalyst 7, the activation barriers seem to be overestimated at the gas-phase DFT and DFT-PCM levels, and underestimated with MP2/6–31G(d) and DFT-D