Remote C-H Bond Functionalizations. Группа авторов
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Название: Remote C-H Bond Functionalizations

Автор: Группа авторов

Издательство: John Wiley & Sons Limited

Жанр: Химия

Серия:

isbn: 9783527824144

isbn:

СКАЧАТЬ resulting in the observed high meta‐selectivity. However, it is worth noting that not all the template assisted meta‐C–H olefination required the use of silver salt, such as the meta‐C–H olefination of benzoic acids by the Li group [28]. In addition, significant effects of distortions of the template were observed in the structural and distortion energy analysis of the transition states, which had help to devise the conformationally flexible directing template for benzoic acids by the groups of Houk and Yu in 2017 [29].

Chemical reaction depicts the proposed catalytic cycle for meta-C–H olefination. Chemical reaction depicts the proposed transition state through computational study.

      Besides the MPAA ligand, the HFIP solvent is another key factor for most of the template assisted meta‐C–H activation reactions. Although the exact role of HFIP is unknown at present, Maiti and coworkers proposed that the solvent HFIP could act as a coordinating ligand in the early stage of the reaction to promote the reaction through experimental and computational investigation [40,54]. Moreover, they also found that the hydrogen‐bonding between HFIP and the pyrimidine‐based template was vital to decrease the basicity of the pyrimidine group and increase the π‐acidity of the Pd center based on nuclear magnetic resonance (NMR) studies [51].

H bonds. The number of transformation types also increases gradually since the first discovery of meta‐C–H olefination. Despite the advances, the directing template strategy still suffers from several limitations. First, the transformation type is still limited, such as amination, fluorination, and alkynylation are not feasible at present. Thus, new protocols with possible new templates are needed. Second, it is not step‐economic to link the template with the substrate with a covalent bond. Although breakthroughs in using catalytic amount of templates have been disclosed, these protocols were limited to special substrates and suffer from limitations such as high metal catalyst loadings and high molecular weights. Therefore, the discovery of more efficient systems using template through non‐covalent interaction is highly desirable. Third, the high catalyst loading and the use of precious metal catalysts are not practical for the application of this method for large scale synthesis. The search for more effective catalytic protocols using low‐cost metal catalysts and even in a low loading is well‐worth investigating. In short, there are still many opportunities for exciting discoveries in the field of meta‐C–H functionalization assisted by directing templates.

      Abbreviations

      AcacetylAlaL‐alanineArarylBoctert‐butyloxycarbonylBnbenzylBubutylCANceric ammonium nitratecat.catalyticCMDconcerted metalation–deprotonationDCE1,2‐dichloroethaneDGdirecting templateDIH1,3‐diiodo‐5,5‐dimethylhydantoinDMFN,N‐dimethylformamideDMPU1,3‐dimethyl‐3,4,5,6‐tetrahydro‐2(1H)‐pyrimidinoneequivequivalentEDGelectron‐donating templateEWGelectron‐withdrawing templateGlyglycineHFIPhexafluoroisopropanolKIEkinetic isotope effectLligandLDAlithium diisopropylamidemmetaMemethylMPAAmono‐N‐protected amino acidNMPN‐methylpyrrolidinoneoorthopparaPhphenylPheL‐phenylalaninePinpinacolPivpivaloylPrpropylTBAtetrabutylammoniumTFAtrifluoroacetic acidTBAPF6tetrabutylammonium hexafluorophosphateTFEtrifluoroethanolTHFtetrahydrofuranXPhos2,4′,6′‐diisopropyl‐1,1′‐biphenyl‐2‐yldicyclohexylphosphine

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