Thermal Rearrangement of 2-Bromooxazolines to 2-Bromoisocyanates

Foltz, Carole; Bellemin‐Laponnaz, Stéphane; Enders, Markus; Wadepohl, Hubert; Gade, Lutz H.

doi:10.1021/ol7027509

Cited by 15 publications

(17 citation statements)

References 32 publications

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“…The latter has been observed in Cu II -and Pd 0/II -catalyzed transformations. [9,13,27,28] The synthesis, crystal structures and magnetic properties of + revealed much lower overall energy differences for the different isomeric forms than found for the mononuclear [Co(iPr-trisox) 2 ] 2 + complexes, as expected considering that the trisox ligands are significantly further removed from each other. [29] The The iron complex 9 is colorless and displays no absorption in the 350-1000 nm range with e > 5 Lmol À1 cm…”

Section: Synthesis and Structural Characterization Of Mononuclear {(Tmentioning

confidence: 58%

Shaping and Enforcing Coordination Spheres: The Implications of C₃ and C₁ Chirality in the Coordination Chemistry of 1,1,1‐Tris(oxazolinyl)ethane (“Trisox”)

Gade

Marconi

Dro

et al. 2007

Chemistry A European J

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A key feature of tris(oxazolinyl)ethane ("trisox") ligands, which have shown broad scope in asymmetric catalysis, is the orientation and steric demand of their oxazoline substituents. This, along with the modularity of their synthesis determines their coordination chemistry. The possibility to combine oxazolines, in which the stereogenic centers adjacent to the N-donor atoms have different absolute configuration, whilst retaining their ability to coordinate as tripodal ligands, has been demonstrated by the synthesis of the enantiomerically pure C3-symmetric iPr-trisox(S,S,S) and C1-symmetric iPr-trisox(S,S,R) and their reaction with [Mo(CO)3(NCMe)3] yielding [Mo{iPr-trisox(S,S,S)}(CO)3] (1 a) and [Mo{iPr-trisox(S,S,R)}(CO)3] (1 b), respectively. The non-autocomplementarity of two homochiral trisox ligands at one metal center has been demonstrated by reaction of rac-C3 iPr-trisox with one equivalent of [Co(ClO4)2].6 H2O, giving the centrosymmetric heterochiral complex [Co(iPr-trisox)2](ClO4)2 (3), whereas an analogous reaction with the enantiopure ligand yielded a mixture of Co(II) complexes, which is characterized by the total absence of a [(trisox)2Co](+/2+) ion. The scope of the trisox ligand in terms of facial coordination to both early and late transition metals was demonstrated by the synthesis and structural characterization of the mononuclear complexes [ScCl3(iPr-trisox)] (4), [Fe(tBu-trisox)(NCMe)3](BF4)2 (5), and [Ru(eta6-p-cymene)(iPr-trisox)](PF6)2 (6). The facial coordination of their three ligating atoms to a metal center may be impeded if the transition-metal center stereoelectronically strongly favors a non-deltahedral coordination sphere, which is generally the case for the heavier d8-transition-metal atoms/ions. Reaction of iPr-trisox with [Rh(cod)2]BF4 led to the formation of the 16-electron d8-configured complex [Rh(iPr-trisox)(cod)](BF4) (7), which is oxidized by CsBr3 to give the Rh(III) complex [RhBr3(iPr-trisox)] (8) possessing a C3-symmetric structure with a kappa3-N-trisox ligand. The crystalline salts [M2(mu-Cl3)(iPr-trisox)2](PF6) (M=Fe(II): 9, Co(II): 10, Ni(II): 11), were prepared by addition of one molar equivalent of iPr-trisox and an excess of KPF6 to solutions of the anhydrous (FeCl2) or hydrated metal halides (CoCl2.6 H2O, NiCl2.6 H2O). All dinuclear complexes display weak magnetic coupling. For the mononuclear species [CuCl2(iPr-trisox)] (12) the removal of a chloride anion and thus the generation of a dinuclear chloro-bridged structure failed due to Jahn-Teller destabilization of a potential octahedral coordination sphere.

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Section: Synthesis and Structural Characterization Of Mononuclear {(Tmentioning

confidence: 58%

Shaping and Enforcing Coordination Spheres: The Implications of C₃ and C₁ Chirality in the Coordination Chemistry of 1,1,1‐Tris(oxazolinyl)ethane (“Trisox”)

Gade

Marconi

Dro

et al. 2007

Chemistry A European J

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“…We begin by summarizing the main experimental findings which form the basis for the reaction mechanism proposed below (Scheme 1). [ 24 ] First, since zero conversion was obtained upon reacting the oxazoline under radical conditions, a radical pathway is excluded. Second, kinetic studies show that the reaction rate is concentration dependent and suggest that the reaction is autocatalyzed.…”

Section: Resultsmentioning

confidence: 99%

“…[ 18–23 ] Interestingly, 2‐bromooxazolines was reported by Foltz et al to thermally and selectively rearrange into 2‐bromoisocyanates in good yields (Figure 2). [ 24 ] Although experimental mechanistic studies were reported, [ 24 ] to the best of our knowledge, a reaction mechanism for this rearrangement has not been reported in the literature. In the present work, we use high‐level G4(MP2) calculations to investigate this rearrangement and propose a detailed reaction mechanism that explains the experimental findings.…”

Section: Introductionmentioning

confidence: 99%

Mechanistic insights into the autocatalyzed rearrangement of 2‐bromooxazolines to 2‐bromoisocyanates by means of high‐level quantum chemical methods

Baroudi

Karton

2021

J of Physical Organic Chem

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A mechanism for the thermal instability and selective rearrangement of 2‐bromooxazolines is proposed and examined using the highly accurate G4(MP2) thermochemical protocol. We propose this rearrangement to be autocatalyzed by bromide ions that are initially formed via a bimolecular reaction between two 2‐bromooxazoline molecules. We find this step to be rate determining, and it results in a consequent and more favorable propagative reaction of bromide ions with the starting material (2‐bromooxazoline). The proposed mechanism sheds light on experimental observations and provides a coherent explanation for 2‐bromooxazolines thermal instability. We proceed to rationalize the high barrier of the rate‐determining step via comparison with experimentally known pathways.

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“…Heterocycles of 1,3‐azoles are important synthetic intermediates, and undergo extensive chemical transformations involving nucleophilic addition of the CN bond or nucleophilic ring‐opening,19 sodium‐alcohol reduction then acid hydrolysis to aldehyde,20 base hydrolysis to organic acid,21 and thermal rearrangement to 2‐bromodifluoromethylisocyanates 22. Therefore, functionalisation of the 1,3‐azolic moiety could provide possibilities for construction of a new generation of gem ‐difluoromethylene‐linked identical or nonidentical twin drugs.…”

Section: Resultsmentioning

confidence: 99%

2011

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Thermal Rearrangement of 2-Bromooxazolines to 2-Bromoisocyanates

Cited by 15 publications

References 32 publications

Shaping and Enforcing Coordination Spheres: The Implications of C₃ and C₁ Chirality in the Coordination Chemistry of 1,1,1‐Tris(oxazolinyl)ethane (“Trisox”)

Shaping and Enforcing Coordination Spheres: The Implications of C₃ and C₁ Chirality in the Coordination Chemistry of 1,1,1‐Tris(oxazolinyl)ethane (“Trisox”)

Mechanistic insights into the autocatalyzed rearrangement of 2‐bromooxazolines to 2‐bromoisocyanates by means of high‐level quantum chemical methods

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Thermal Rearrangement of 2-Bromooxazolines to 2-Bromoisocyanates

Cited by 15 publications

References 32 publications

Shaping and Enforcing Coordination Spheres: The Implications of C3 and C1 Chirality in the Coordination Chemistry of 1,1,1‐Tris(oxazolinyl)ethane (“Trisox”)

Shaping and Enforcing Coordination Spheres: The Implications of C3 and C1 Chirality in the Coordination Chemistry of 1,1,1‐Tris(oxazolinyl)ethane (“Trisox”)

Mechanistic insights into the autocatalyzed rearrangement of 2‐bromooxazolines to 2‐bromoisocyanates by means of high‐level quantum chemical methods

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Shaping and Enforcing Coordination Spheres: The Implications of C₃ and C₁ Chirality in the Coordination Chemistry of 1,1,1‐Tris(oxazolinyl)ethane (“Trisox”)

Shaping and Enforcing Coordination Spheres: The Implications of C₃ and C₁ Chirality in the Coordination Chemistry of 1,1,1‐Tris(oxazolinyl)ethane (“Trisox”)