- Transition Metal-Catalysed Intramolecular Carbenoid C?H Insertion for Pyrrolidine Formation by Decomposition of α-Diazoesters
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The use of Pd-, Rh(II)- and Ru(II)-based catalysts has been explored in the transition metal-catalysed intramolecular carbenoid C?H insertion of α-diazoesters leading to pyrrolidines. Although the outcome of the reaction was highly substrate-dependent, in general, it was possible to control the chemoselectivity of the process towards pyrrolidines by adequate catalyst selection. The Pd(0)-catalysts were as efficient as [Rh(Ph3CCO2)2]2 in promoting the C(sp3)?H insertion of ortho-substituted anilines. In contrast, for anilines bearing meta- and para-substituents, the Rh(II)-catalyst provided the best chemoselectivities and reaction yields. On the other hand, [Ru(p-cymene)Cl2]2 was the most efficient catalyst for the insertion reaction of the N-benzyl-N-phenyl and N,N-dibenzyl α-diazoesters, while the C(sp3)?H insertion of the N-benzylsulfonamide substrate was only promoted by [Rh(Ph3CCO2)2]2. According to density functional theory (DFT) calculations, the mechanism involved in the Pd(0)- and Ru(II)-catalysed C(sp3)?H insertions differs considerably from that typically proposed for the Rh(II)-catalysed transformation. Whereas the Pd(0)-catalysed reaction involves a Pd-mediated 1,5-H migration from the C(sp3)?H bond to the carbenoid carbon atom leading to the formal oxidation of the transition metal, a Ru(II)-promoted Mannich type reaction involving a zwitterionic intermediate seems to be operative in the Ru(II)-catalysed transformation. (Figure presented.).
- Solé, Daniel,Amenta, Arianna,Mariani, Francesco,Bennasar, M.-Llu?sa,Fernández, Israel
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- Palladium-catalyzed intramolecular carbene insertion into C(sp3)-H bonds
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A palladium-catalyzed carbene insertion into C(sp3)-H bonds leading to pyrrolidines was developed. The coupling reaction can be catalyzed by both Pd0 and PdII, is regioselective, and shows a broad functional group tolerance. This reaction is the first example of palladium-catalyzed C(sp3)-C(sp3) bond assembly starting from diazocarbonyl compounds. DFT calculations revealed that this direct C(sp3)-H bond functionalization reaction involves an unprecedented concerted metalation-deprotonation step. Pd in action: Palladium has been used to catalyze the C(sp3)-H insertion of metal carbenoids derived from α-diazoesters to form pyrrolidines through intramolecular assembly of C(sp3)-C(sp3) bonds. A reaction mechanism involving a metalation-deprotonation step instead of the usual concerted but asynchronous process is proposed.
- Solé, Daniel,Mariani, Francesco,Bennasar, M.-Llu?sa,Fernández, Israel
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p. 6467 - 6470
(2016/06/01)
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- The coupling of tertiary amines with acrylate derivatives via visible-light photoredox catalysis
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Catalyzed by Ru(bpy)3(BF4)2, the photoredox coupling of tertiary amines with acrylate derivatives including Baylis-Hillman adducts under visible light irradiation was successfully established. The scope of the substrates w
- Dai, Xiaojun,Cheng, Dongping,Guan, Baochuan,Mao, Wenjuan,Xu, Xiaoliang,Li, Xiaonian
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p. 7212 - 7219
(2014/08/18)
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