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5 article(s) from Maas, Gerhard

Reactions of 3-aryl-1-(trifluoromethyl)prop-2-yn-1-iminium salts with 1,3-dienes and styrenes

Thomas Schneider,
Michael Keim,
Bianca Seitz and
Gerhard Maas

Beilstein J. Org. Chem. 2020, 16, 2064–2072, doi:10.3762/bjoc.16.173

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Scheme 1: Diels–Alder reaction of propyn-1-iminium salt 1a compared with the reported [29] reaction of 4-phenyl-1...

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Scheme 2: Sequential Diels–Alder/intramolecular S_E(Ar) reaction of propyn-1-iminium triflates 1a,b. Condition...

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Scheme 3: Diels–Alder reaction of 1a and anthracene followed by an intramolecular S_E(Ar) reaction.

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Figure 1: Solid-state molecular structure of 11 (ORTEP plot).

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Scheme 4: Reactions of propyn-1-iminium salt 1a with styrenes.

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Figure 2: Solid-state molecular structure of 12c (ORTEP plot).

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Figure 3: Solid-state molecular structure of 12d (ORTEP plot). Both the R and the S enantiomer are present in...

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Scheme 5: A mechanistic proposal for the reaction of alkyne 1a with styrenes.

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Scheme 6: Reaction of alkyne 1a with 1,2-dihydronaphthalene.

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Scheme 7: Synthesis and solid-state molecular structure (ORTEP plot) of pentafulvene 19; selected bond distan...

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Scheme 8: Proposed mechanistic pathway leading to fulvene 19.

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Published 24 Aug 2020

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1,5-Phosphonium betaines from N-triflylpropiolamides, triphenylphosphane, and active methylene compounds

Vito A. Fiore,
Chiara Freisler and
Gerhard Maas

Beilstein J. Org. Chem. 2019, 15, 2603–2611, doi:10.3762/bjoc.15.253

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Scheme 1: Stable betaines I–IV.

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Scheme 2: Reactions of N-triflyl-propiolamides 1 with N- and P-nucleophiles. Tf = SO₂CF₃.

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Scheme 3: Synthesis of betaines 3 by a three-component reaction. N-triflylpropiolamides 1: R = Ph (a), 4-Cl-C₆...

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Figure 1: Phosphonium betaines 3 prepared. An E:Z ratio of 100:0 means that only the E-isomer was observed in...

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Scheme 4: Unexpected synthesis of E-3o.

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Scheme 5: Betaines 3 from propiolic acid chlorides.

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Scheme 6: Two mechanistic scenarios for the formation of betaines 3.

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Figure 2: Solid-state structure of E-3a (ORTEP plot), two symmetry-independent molecules in the triclinic uni...

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Figure 3: Solid-state structure of E-3b·CH₂Cl₂ (ORTEP plot); CH₂Cl₂ solvate molecule not shown.

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Figure 4: Solid-state structure of E-3e·H₂O·CH₂Cl₂ (ORTEP plot). The CH₂Cl₂ solvate molecule is disordered. H...

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Figure 5: Solid-state structure of Z-3e (ORTEP plot).

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Scheme 7: Resonance structures describing the bonding in 1,2-oxaphospholes/1,5-betaines 8.

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Published 01 Nov 2019

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Derivatives of the triaminoguanidinium ion, 5. Acylation of triaminoguanidines leading to symmetrical tris(acylamino)guanidines and mesoionic 1,2,4-triazolium-3-aminides

Jan Szabo,
Julian Greiner and
Gerhard Maas

Beilstein J. Org. Chem. 2017, 13, 579–588, doi:10.3762/bjoc.13.57

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Scheme 1: Reactions of aminoguanidines with carboxylic acids and acid chlorides. The structural formulae show...

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Scheme 2: Threefold N-acylation of triaminoguanidinium chloride (1) with acyl chloride 2b.

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Scheme 3: Reaction of 1,2,3-tris(benzylamino)guanidinium salts 4 and 5 with acyl chlorides to give 1,2,3-tris...

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Figure 1: Molecular structure of 6b·2C₂H₅OH in the solid state, with numbering of atoms (ORTEP plot). Selecte...

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Scheme 4: Protonation and methylation of 1,2,4-triazolium-3-aminides 7b,c.

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Scheme 5: Catalytic hydrogenation/debenzylation of betaines 7.

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Figure 2: Left: molecular structure of 8b in the solid state (OLEX2 plot). Right: crystal structure viewed al...

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Figure 3: Left: solid-state structure of 9b·H₂O (ORTEP plot). Right: centrosymmetric hydrogen-bonded dimer of...

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Figure 4: Solid-state structure of mesoionic compound 7a (ORTEP plot); thermal displacement ellipsoids are dr...

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Figure 5: UV–vis spectra of 7a–d in chloroform (c = 0.04 mmol L⁻¹); λ_max [nm] (ε [L mol⁻¹ cm⁻¹]): 7a: 350 (47...

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Published 22 Mar 2017

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Derivatives of the triaminoguanidinium ion, 3. Multiple N-functionalization of the triaminoguanidinium ion with isocyanates and isothiocyanates

Jan Szabo,
Kerstin Karger,
Nicolas Bucher and
Gerhard Maas

Beilstein J. Org. Chem. 2014, 10, 2255–2262, doi:10.3762/bjoc.10.234

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Scheme 1: Conditions: a) benzaldehyde, ethanol/water, reflux, 1 h, 96% yield; b) H₂, Pd/C (10%), MeOH, rt, 48...

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Scheme 2: Carbamoylation of 1,2,3-tris(benzylamino)guanidinium salts 3 and 5-OTs.

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Figure 1: Solid-state structure of 7a·3CH₃CN. Left: Molecular structure with numbering of atoms. Right: N–H··...

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Scheme 3: Deprotonation of 7a to yield the neutral guanidine derivative 8.

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Figure 2: Solid-state structure of 8. Thermal displacement ellipsoids are drawn at the 20% probability level....

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Scheme 4: Sulfonylcarbamoylation of salt 3.

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Figure 3: Hydrogen-bonded one-dimensional network of guanidine 8 in the solid state. The intramolecular N9···...

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Scheme 5: Reaction of 1,2,3-trisbenzylaminoguanidinium chloride (3) with aryl isothiocyanates.

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Figure 4: Solid-state structure of 10b. Thermal displacement ellipsoids are drawn at the 30% probability leve...

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Scheme 6: Proposed mechanism of the formation of 10 and 11.

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Published 24 Sep 2014

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Intramolecular carbenoid ylide forming reactions of 2-diazo-3-keto-4-phthalimidocarboxylic esters derived from methionine and cysteine

Marc Enßle,
Stefan Buck,
Roland Werz and
Gerhard Maas

Beilstein J. Org. Chem. 2012, 8, 433–440, doi:10.3762/bjoc.8.49

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Scheme 1: Synthesis of cyclic sulfonium ylides 2; n = 0–3.

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Scheme 2: Non-carbenoid formation of sulfonium ylide 4.

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Scheme 3: Conditions: (a) phthalic anhydride, NEt₃ (10 mol %), toluene, reflux, 2 h; (b) 1. carbonyldiimidazo...

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Scheme 4: Rh(II)-catalysed carbenoid reactions of diazoesters 8a,b.

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Figure 1: Proposed relative configurations of the diastereomeric cyclic sulfonium ylides 12aA and 12aB. ¹H NM...

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Scheme 5: Endo transition state for [3 + 3]-dimerisation of carbonyl ylide 14.

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Scheme 6: Rh(II)-catalysed carbenoid reactions of diazoester 8c.

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Scheme 7: Tandem cyclisation/intermolecular cycloaddition of diazoester 8a. Conditions: (a) Rh₂(OAc)₄ (3 mol ...

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Scheme 8: Carbenoid formation of sulfonium ylides from diazoesters 11a,b. Conditions: (a) Rh₂(OAc)₄ (3 mol %)...

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Published 22 Mar 2012

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