On the mechanism of imine elimination from Fischer tungsten carbene complexes

• Philipp Veit,
• Christoph Förster and
• Katja Heinze

Beilstein J. Org. Chem. 2016, 12, 1322–1333, doi:10.3762/bjoc.12.125

• ligand [Fc-C=N-Fc]– (15–) as further alternative (pathway 3c, Scheme 4). The calculated Gibbs free energies for W(CO)5(E-2) and W(CO)5(Z-2) are basically identical (Supporting Information File 1, Figure S16, Scheme 3). The calculated barrier for the E/Z isomerization W(CO)5(E-2) → W(CO)5(Z-2) amounts to

• (carbene)–N moiety. This reaction coordinate is fully analogous to the proposed mechanism of the E/Z isomerization of imines [66][67]. During the 1,2-H-shift of E-2 to E-3, the migrating hydrogen atom interacts with the empty pπ-type orbital of the carbene carbon atom (ΔG‡ = 250 kJ mol−1), which is in

• with the hydrogen 1s orbital. Because of the non-crossing rule, this path is symmetry forbidden for aromatic carbenes [47][72]. The calculated barrier of the E/Z isomerization Z-3 → E-3 (ΔG‡ = 52 kJ mol−1) is in good agreement with experimental data for other imines with similar steric bulk, e.g., (Fc

Cupreines and cupreidines: an established class of bifunctional cinchona organocatalysts

• Laura A. Bryant,
• Rossana Fanelli and
• Alexander J. A. Cobb

Beilstein J. Org. Chem. 2016, 12, 429–443, doi:10.3762/bjoc.12.46

• utilized a 9-OH benzoyl derivatised cupreine CPN-38 to effect a Friedel-Crafts reaction of 2-naphthols 36 with benzoxathiazine 2,2-dioxides 37 (Scheme 10). These cyclic imides, derived from salicylic aldehydes, have a rigid structure which prevents E/Z-isomerization, allowing for greater control over the

Synthesis of photoresponsive cholesterol-based azobenzene organogels: dependence on different spacer lengths

• Yuchun Ren,
• Bin Wang and
• Xiuqing Zhang

Beilstein J. Org. Chem. 2015, 11, 1089–1095, doi:10.3762/bjoc.11.122

• can bring about new predictable gelation abilities for the construction of novel cholesterol-based gelators. Azobenzene is one of the smartest molecules among all known photochromic compounds because of its E/Z isomerization [18]. Based on this, photomechanical soft materials containing azobenzene

Photoswitchable precision glycooligomers and their lectin binding

• Daniela Ponader,
• Sinaida Igde,
• Marko Wehle,
• Katharina Märker,
• Mark Santer,
• David Bléger and
• Laura Hartmann

Beilstein J. Org. Chem. 2014, 10, 1603–1612, doi:10.3762/bjoc.10.166

• were dissolved in the buffer used for the SPR measurements, see Supporting Information File 1 for the details) were irradiated at λ = 360 nm to induce the E → Z isomerization. The typical decrease of the π→π* band at 330 nm and increase of the n→π* band centered at 440 nm was observed in the UV–vis

Olefin cross metathesis based de novo synthesis of a partially protected L-amicetose and a fully protected L-cinerulose derivative

• Bernd Schmidt and
• Sylvia Hauke

Beilstein J. Org. Chem. 2014, 10, 1023–1031, doi:10.3762/bjoc.10.102

• benzoylation in pyridine resulted exclusively in the formation of furan 10 (Table 2, entry 1). We reasoned that pyridine initiates an E/Z-isomerization of the enal through nucleophilic attack at the β-position, followed by lactol formation, benzoylation of the lactol and finally elimination of benzoic acid

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

• −284.0 cm−1 (TS1) and −362.2 cm−1 (TS2) in the gas phase). This imaginary frequency belongs to the rotational vibration of the formyl hydrogen and the formyl oxygen along the reaction pathway for the E/Z isomerization of 4. In both transition states geometries, the C–N bond (143 pm) is significantly

Design and synthesis of a photoswitchable guanidine catalyst

• Philipp Viehmann and
• Stefan Hecht

Beilstein J. Org. Chem. 2012, 8, 1825–1830, doi:10.3762/bjoc.8.209

• undergo photoinduced E→Z isomerization, allowing the Brønsted acceptor, in this case a ketone, to form a hydrogen-bridge to the proton of the guanidine. Results and Discussion The synthesis of guanidine 2E (Scheme 3) was accomplished starting from phenylisocyanate (3) and 3-nitroaniline (6). The latter

• ellipsoids (CCDC 891016). UV–vis spectra of guanidine 2 in acetonitrile, c = 3.9·10−5 mol/L. (a) E→Z isomerization with irradiation at 340 nm, 25 °C; (b) Z→E isomerization with irradiation at 254 nm, 25 °C; (c) thermal Z→E isomerization at 40 °C; (d) spectra of 2E (blue) and 2Z (calculated, red). Supposed

meta-Oligoazobiphenyls – synthesis via site-selective Mills reaction and photochemical properties

• Raphael Reuter and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2012, 8, 877–883, doi:10.3762/bjoc.8.99

• absorption of the whole spectrum is noted due to the additional chromophore in the molecule. Upon irradiation at 356 nm (8 W hand-held UV lamp, at room temperature) all compounds underwent an E→Z isomerization, which can be seen as a decrease of the π–π* and an increase of the n–π* band. In this respect all

The importance of the rotor in hydrazone-based molecular switches

• Xin Su,
• Timo Lessing and
• Ivan Aprahamian

Beilstein J. Org. Chem. 2012, 8, 872–876, doi:10.3762/bjoc.8.98

• Xin Su Timo Lessing Ivan Aprahamian Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755, United States Department of Chemistry, Heinrich-Heine-Universität Düsseldorf, Universitätsstr. 1, 40225 Düsseldorf, Germany 10.3762/bjoc.8.98 Abstract The pH-activated E/Z isomerization

• of a series of hydrazone-based systems having different functional groups as part of the rotor (R = COMe, CN, Me, H), was studied. The switching efficiency of these systems was compared to that of a hydrazone-based molecular switch (R = COOEt) whose E/Z isomerization is fully reversible. It was found

• their configuration (i.e., E/Z isomerization) as a function of pH [22][23][24], or upon the addition of a Lewis acid (i.e., Zn2+) [25]. The simplest hydrazone switch (PPH-1, Scheme 1) for example, exists mainly as its E isomer (PPH-1-E) in solution, as illustrated by the E/Z isomer ratio of 93:7 in

Effects of anion complexation on the photoreactivity of bisureido- and bisthioureido-substituted dibenzobarrelene derivatives

• Heiko Ihmels and
• Jia Luo

Beilstein J. Org. Chem. 2011, 7, 278–289, doi:10.3762/bjoc.7.37

• nm) in the gas phase, and the latter compound is able to sensitize a triplet-state E/Z-isomerization of alkenes [48]. On the other hand, the thioureido-substituted dibenzobarrelene derivative 1i does not undergo a DPM rearrangement upon direct irradiation, despite the potentially sensitizing 3,5-bis