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].
Scheme 2.65 Proposed catalytic cycle for meta‐C–H olefination.
Scheme 2.66 Proposed transition state through computational study.
Subsequently, Houk, Yu, Wu, and coworkers revealed the dual roles of the amino acid ligand in improving reactivity and selectivity through mass spectrometry (MS) and DFT calculations [56]. It was found that the amino acid ligand aced as both a dianionic ligand and a proton acceptor, leading to the stabilization of the monomeric Pd complexes and serving as the internal base for proton abstraction through a CMD pathway.
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].
2.4 Conclusion
Since 2012, the directing template approach has promoted a range of meta‐selective C–H activation reactions with several classes of substrate. Three major classes of directing templates have been engineered by recognition of the geometry and distance between the directing atom and the target meta‐C
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
References
1 1 Truong, T. and Daugulis, O. (2012). Angew. Chem. Int. Ed. 51: 11677.
2 2 Julia‐Hernandez, F., Simonetti, M., and Larrosa, I. (2013). Angew. Chem. Int. Ed. 52: 11458.
3 3 Ackermann, L. and Li, J. (2015). Nat. Chem. 7: 686.
4 4 Frost, C.G. and Paterson, A.J. (2015). ACS Cent. Sci. 1: 418.
5 5 Li, J., De Sarkar, S., and Ackermann, L. (2016). Top. Organomet. Chem. 55: 217.
6 6 Yang, J. (2015). Org. Biomol. Chem. 13: 1930.
7 7 Chattopadhyay, B. and Bisht, R. (2016). Synlett 27: 2043.
8 8 Dey, A., Agasti, S., and Maiti, D. (2016). Org. Biomol. Chem. 14: 5440.
9 9 Ghosh, M. and De Sarkar, S. (2018). Asian J. Org. Chem. 7: 1236.
10 10 Dey, A., Sinha, S.K., Achar, T.K., and Maiti, D. (2019). Angew. Chem. Int. Ed. 58: 10820.
11 11 Leow, D., Li, G., Mei, T.S., and Yu, J.‐Q. (2012). Nature 486: 518.
12 12 Zhang, Z., Tanaka, K., and Yu, J.‐Q. (2017). Nature 543: 538.
13 13 Achar, T.K., Ramakrishna, K., Pal, T. et al. (2018). Chem. Eur. J. 24: 17906.
14 14 Modak, A., Mondal, A., Watile, R. et al. (2016). Chem. Commun. 52: 13916.
15 15 Li, S., Wang, H., Weng, Y., and Li, G. (2019). Angew. Chem. Int. Ed. https://doi.org/10.1002/anie.201910691.
16 16 Xu, H.‐J., Lu, Y., Farmer, M.E. et al. (2017). J. Am. Chem. Soc. 139: 2200.
17 17 Xu, H.‐J., Kang, Y.‐S., Shi, H. et al. (2019). J. Am. Chem. Soc. 141: 76.
18 18 Wan, L., Dastbaravardeh, N., Li, G., and Yu, J.‐Q. (2013). J. Am. Chem. Soc. 135: 18056.
19 19 Xu, H., Liu, M., Li, L.J. et al. (2019). Org. Lett. 21: 4887.
20 20 Bera, M., Modak, A., Patra, T. et al. (2014). Org. Lett. 16: 5760.
21 21 Deng, Y. and Yu, J.‐Q. (2015). Angew. Chem. Int. Ed. 54: 888.
22 22 Bera, M., Agasti, S., Chowdhury, R. et al. (2017). Angew. Chem. Int. Ed. 56: 5272.
23 23 Jin, Z., Chu, L., Chen, Y.‐Q., and Yu, J.‐Q. (2018). Org. Lett. 20: 425.
24 24 Brochetta, M., Borsari, T., Bag, S. et al. (2019). Chem. Eur. J. 25: 10323.
25 25 Jiao, B., Peng, Z., Dai, Z.‐H. et al. (2019). Eur. J. Org. Chem. 2019: 3195.
26 26 Bag, S., Petzold, M., Sur, A. et al. (2019). Chem. Eur. J. 25: 9433.
27 27 Achar, T.K., Zhang, X., Mondal, R. et al. (2019). Angew. Chem. Int. Ed. 58: 10353.
28 28
