1,4‐Conjugate Addition of Aryl boronic Acids on Cyclohexenone as Catalyzed by Rhodium(I) Complexes of C₂‐Symmetric Bioxazoline Fused N‐heterocyclic Carbenes

Abstract

Rhodium(I) complexes (1‐3) of chiral C2‐symmetric tricyclic bioxazoline fused imidazole derived N‐heterocyclic carbene ligands were efficient precatalysts for the 1,4‐conjugate addition of aryl boronic acids to cyclohexenone yielding 3‐aryl cyclohexanones in moderate to excellent yields but without any chirality transfer. Quite significantly, the intermediates of the proposed catalytic cycle namely, a rhodium hydroxo species (A), a phenyl bound rhodium species (B) and a 3‐phenyl cyclohexenolate bound rhodium species (D) have been detected by mass spectrometry. Lastly, the rhodium(I) precatalysts of the type, {(3R,7R)‐3,7‐di‐R‐2,3,7,8‐tetrahydrodioxazolo[3,2‐c:3′,2′‐e]imidazol‐5‐ylidene}Rh(COD)Cl, [R=s‐butyl (1), i‐butyl (2), i‐propyl (3), COD=1, 5‐cyclooctadiene] were prepared by the direct metalation of tricyclic oxazoline fused imidazole derived N‐heterocyclic carbene precursors namely, (3R,7R)‐3,7‐di‐R‐2,3,7,8‐tetrahydrodioxazolo[3,2‐c:3′,2′‐e]imidazol‐4‐ium trifluoromethanesulfonate, [R=s‐butyl, i‐butyl, i‐propyl] with {(COD)RhCl}2 in presence of t‐BuOK at room temperature.

Simple synthetic access to [Au(IBiox)Cl] complexes

“…Consequently, only a limited number of reports have dealt with the synthesis of IBiox metal complexes. 4,7,[9][10][11][12][13][14] For instance [Pd(IBiox)Cl 2 ] 2 complexes were synthesized using IBiox•HOTf salts, Pd(OAc) 2 and LiCl, in THF at 100 °C for 16 h. 4,9 Another complex, [Pd(IBiox i Pr) 2 I 2 ], one where two IBiox ligands are bound to the metal was obtained using the IBiox triflate salt and Pd(OAc) 2 , with KO t Bu as base in THF as solvent. 7 [Pd(IBiox)(π-allyl)Cl] complexes have also been synthesized using a strong base, NaO t Bu, in dimethoxyethane (DME).…”

“…11 In addition, complexes with the general formula [Rh(IBiox)(L)Cl] (L = COE, NBD, COD) are also reported again via free carbene route with the use of strong bases (KO t Bu) in benzene. 11,12 Other examples of [M(IBiox)(CO) 2 Cl] (M = Rh, Ir) complexes can be found in the literature, synthesized via the transmetallation pathway from [Ag(IBiox)Br] in the case of rhodium, 13 and via the free carbene route for the Ir complex. 4 To the best of our knowledge, there is only one example of gold-IBiox complex, which was synthesized from IBiox•HOTf salt with AuCl in the presence of NaO t Bu in THF under inert atmosphere.…”

Colorimetric Fluorescence of a 2,4,5‐Triaryl Imidazole‐Based Sensor for the Selective Detection of Iron

“…[27][28][29][30][31][32] Attachment of a strong suction or donor group to an imidazole ring causes intramolecular charge transfer (ICT). [33][34][35] Therefore, most of the compounds based on the structure of imidazole have superior luminescence properties. In addition, the bipolar structure of this push-pull electron gives imidazole derivatives more easily regulated photophysical and chemical properties.…”

Accessing Heteroannular Benzoxazole and Benzimidazole Scaffolds via Carbodiimides Using Azide–Isocyanide Cross-Coupling as Catalyzed by Mesoionic Singlet Palladium Carbene Complexes Derived from a Phenothiazine Moiety

“…With our interest in exploring the potentials of the transition metal complexes of the heteroatom stabilized cyclic and acyclic singlet carbene ligands in homogeneous catalysis − and in biomedical applications, we study different singlet-carbene ligand classes covering the cyclic normal N-heterocyclic carbenes, abnormal mesoionic carbenes , the acyclic diaminocarbenes , and the fused-cyclic ones of the imidazole, benzimidazole, triazole, ,, oxazolidine, bioxazoline, and triazolooxazine architectures. The mesoionic (MIC) carbenes, featuring less heteroatom stabilization than the more ubiquitous normal N-heterocyclic carbenes, come with specific donors and reactivity properties but surprisingly remain less explored .…”