Evolution of N-Heterocycle-Substituted Iodoarenes (NHIAs) to Efficient Organocatalysts in Iodine(I/III)-Mediated Oxidative Transformations
The reactivity of ortho-functionalized N-heterocycle-substituted iodoarenes (NHIAs) as organocatalysts in iodine(I/III)-mediated oxidations was systematically investigated in the α-tosyloxylation of ketones as the model reaction. During a systematic catalyst evolution, it was found that NH-triazoles and benzoxazoles have the most significant positive influence on the reactivity of the central iodine atom. A further catalyst improvement which focused on the substitution pattern of the arene revealed a remarkable ortho-effect. By introduction of an o-OMe group we were able to generate a novel NHIA with a so far unseen catalytic efficiency. This new catalyst is not only easy to synthesize but also enabled the α-tosyloxylation of carbonyl compounds at the lowest reported catalyst loading of only 1 mol%. Finally, the performance of this iodine(I) catalyst was successfully demonstrated in intramolecular oxidative couplings of biphenyls and oxidative rearrangements. (Figure presented.).
Boelke, Andreas,Nachtsheim, Boris J.
p. 184 - 191
(2019/12/11)
Revisiting the Gold-Catalyzed Dimerization of 2-Ethynylanilines: A Room-Temperature and Silver-Free Protocol for the Synthesis of Multifunctional Quinolines
A room temperature and silver-free protocol for the formation of quinolines from 2-ethynylanilines through a dimerization event was achieved using a dinuclear gold catalyst, Au2(BIPHEP)(NTf2)2. The reaction is inherently modular, allowing for the incorporation of peripheral substituents at any site of the quinoline product. The reaction is readily applied to other heterocyles also as exemplified by the preparation of naphthyridines. Competition reactions to determine the reactivity of dissimilar alkynes demonstrated that the product ratio of dimerization vs intermolecular addition is rather dependent on the electronic nature of aryl substituent on the alkynes. However, control experiments with substrates possessing internal alkynes resulted in cycloisomerization instead of expected dimerization, which is indicative of possible steric influence of the alkyne terminus in the reaction outcome.
Praveen, Chandrasekar,Perumal
p. 855 - 864
(2016/03/15)
Au-catalyzed formation of functionalized quinolines from 2-alkynyl arylazide derivatives
A new method for converting 2-alkynyl arylazide derivatives into functionalized polysubstituted quinolines following a gold-catalyzed 1,3-acetoxy shift/cyclization/1,2-group shift sequence has been developed. This transformation proceeds under mild reaction conditions, is efficient, and tolerates a large variety of functional groups.