Diastereoselectivity in the Staudinger reaction of pentafluorosulfanylaldimines and ketimines

• Alexander Penger,
• Cortney N. von Hahmann,
• Alexander S. Filatov and
• John T. Welch

Beilstein J. Org. Chem. 2013, 9, 2675–2680, doi:10.3762/bjoc.9.303

• group as shown in A. Cornforth control of the ring closure step of the zwitterion (B in Scheme 4) where the SF5 would be antiperiplanar to the iminium ion would lead to the observed diastereoselectivity (Scheme 1). This finding is consistent with dipolar effects being most important in reactions with

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

• conditions leading to loss of stereointegrity. However, a more likely explanation is that cycloaddition occurs by a stepwise process involving a tin(IV)-coordinated zwitterion intermediate. The reaction with pure Z-diene 1b gave significantly different results. Only four cycloadducts were obtained, all of

• nitroalkene Diels–Alder reactions have been proposed. Denmark et al. favor a stepwise process proceeding via a zwitterion intermediate [11][14]. Alkene stereointegrity is normally retained, presumably owing to a cyclic conformation dictated by charge interaction between the cation center and tin nitronate

Presence or absence of a novel charge-transfer complex in the base-catalyzed hydrolysis of N-ethylbenzamide or ethyl benzoate

• Shinichi Yamabe,
• Wei Guan and
• Shigeyoshi Sakaki

Beilstein J. Org. Chem. 2013, 9, 185–196, doi:10.3762/bjoc.9.22

• of the carbonyl 18O exchange and D2O solvent kinetic isotope effects [21][22][23][24][25]. They suggested intervention of a pair of a zwitterion and OH− as well as that of the anionic tetrahedral intermediate (Scheme 1). Although many theoretical studies of the basic amide hydrolysis have been

• reported so far [26][27][28][29][30][31][32][33][34][35][36][37], the presence or absence of the zwitterion has not been scrutinized. As for zwitterions of amino acids and peptides, the effect of the solvent on the structure and various spectra has been examined carefully [38][39][40][41][42][43][44][45

• ][46]. Explicit solvent models were reported to be necessary, and it was shown that the use of continuum solvent models is not adequate. For instance, Degtyarenko and co-workers demonstrated that 20 water molecules are needed to completely solvate the L-alanine zwitterion [46]. The average number of

Polar reactions of acyclic conjugated bisallenes

• Reiner Stamm and
• Henning Hopf

Beilstein J. Org. Chem. 2013, 9, 36–48, doi:10.3762/bjoc.9.5

• data (Supporting Information File 1) also agree with the structural proposal 72. For the formation of the two reaction products we suggest the pathways given in Scheme 14. The initial adduct of CSI to 2 is again a zwitterion 70. This either cycloisomerizes to the β-lactam 71 or undergoes an

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

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

• cyclopentenones [140]. Applying the mechanism discussed in this latter context to 24, it is reasonable to propose the formation of an allene-epoxide first [141], which can exist either in a transoid, 212, or cisoid conformation, 213 (Scheme 51). Whereas the former could open up to the “stretched” zwitterion 214

Carbohydrate-auxiliary assisted preparation of enantiopure 1,2-oxazine derivatives and aminopolyols

• Marcin Jasiński,
• Dieter Lentz and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2012, 8, 662–674, doi:10.3762/bjoc.8.74

• case, led to the formation of methyl acrylate and imine J. This imine underwent subsequent cyclisation to zwitterion K and two proton shifts, probably via 3-exomethylene compound L, finally led to pyrrole 5. This mechanism is certainly speculative but offers a possibility to explain the formation of

Acid catalyzed cyclodimerization of 2,2-bis(trifluoromethyl)-4-alkoxy-oxetanes and -thietanes. Synthesis of 2,2,6,6-tetrakis(trifluoromethyl)-4,8-dialkoxy-1,5-dioxocanes and 3,3,7,7-tetrakis(trifluoromethyl)-9-oxa-2,6-dithia-bicyclo[3.3.1]nonane

• Viacheslav A. Petrov and
• Will Marshall

Beilstein J. Org. Chem. 2010, 6, No. 46, doi:10.3762/bjoc.6.46

• and alcohols, is presented by Scheme 5. Coordination of the Lewis acid with the oxetane ring oxygen results in the formation of stabilized zwitterion A, which probably exists in equilibrium with the starting material. The reaction of A with a second mole of oxetane then leads to the formation of

• zwitterion B, which can undergo intramolecular cyclization with formation of 1,5-dioxocanes 2a–c. The Lewis acid liberated in this process is free to carry out the next catalytic cycle. It should be pointed out, that recently a zwitterion similar to B was observed in the isomerization of the cycloadduct of

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

Comparison of zwitterionic N-alkylaminomethanesulfonic acids to related compounds in the Good buffer series

• Robert D. Long,
• Newton P. Hilliard Jr,
• Suneel A. Chhatre,
• Tatiana V. Timofeeva,
• Andrey A. Yakovenko,
• Daniel K. Dei and
• Enoch A. Mensah

Beilstein J. Org. Chem. 2010, 6, No. 31, doi:10.3762/bjoc.6.31

• unstable at elevated temperature (as when autoclaving) – thus limiting their utility. Keywords: aminomethanesulfonate buffers; Good buffer; morpholinomethanesulfonic acid; pKa comparison; zwitterion; Introduction Some of the most widely used biological buffers are the compounds based on tertiary and

• sulfonic acid and amino group is if the zwitterion is formed by protonation at the piperazine nitrogen that is bonded to the hydroxyethyl functional group. This nitrogen’s basicity would be expected to be only slightly impacted by structural modifications of the alkylsulfonic acid group at the other

• nitrogen. This hypothesis is supported by the crystal structure of HEPMS 2 as a zwitterion shown in Figure 4. The crystal structure of 2 is consistent with the one previously reported for HEPES [11]. Both have piperazine rings in the chair conformation, with extended conformation for the side chains. Both

Self-association of an indole based guanidinium-carboxylate-zwitterion: formation of stable dimers in solution and the solid state

• Carolin Rether,
• Wilhelm Sicking,
• Roland Boese and
• Carsten Schmuck

Beilstein J. Org. Chem. 2010, 6, No. 3, doi:10.3762/bjoc.6.3

• , 45141 Essen, Germany 10.3762/bjoc.6.3 Abstract The indole based zwitterion 2 forms stable dimers held together by H-bond assisted ion pairs. Dimerisation was confirmed in the solid state and studied in solution using dilution NMR experiments. Even though zwitterion 2 forms very stable dimers even in

• DMSO, their stability is lower than of an analogous pyrrole based zwitterion 1. As revealed by the X-ray crystal structure the two binding sites in 2 cannot be planar due to steric interactions between the guanidinium group and a neighbouring aromatic CH. Hence the guanidinium moiety is twisted out of

• -complementary zwitterions that from stable aggregates in polar solution based on H-bond assisted ion pair formation. A few years ago we introduced the guanidiniocarbonyl pyrrole carboxylate zwitterion 1 which forms extremely stable dimers not only in the solid state but also in polar solution [12]. In DMSO the

Synthesis of novel (1-alkanoyloxy- 4-alkanoylaminobutylidene)-1,1-bisphosphonic acid derivatives

• Petri A. Turhanen and
• Jouko J. Vepsäläinen

Beilstein J. Org. Chem. 2006, 2, No. 2, doi:10.1186/1860-5397-2-2

• , 6.3, 10.9 and 12.2 (Ezra et al. [26]), exists as a zwitterion (see Figure 1) and the ammonium group is protected against electrophilic attack of the acyl group. Also the mono sodium salt of alendronic acid was a poor starting material due to the same reason but ca. 37% of 2a was obtained. As expected

• when an excess of anhydride was used. Since the amine group of alendronic acid is protected due to zwitterion, we attempted to acetylate the middle carbon OH-group directly by using alendronic acid and its monosodium salt under dry conditions, as we did for etidronic acid, [27] but unfortunately this