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Review
. 2018 Aug 6;8(49):27881-27891.
doi: 10.1039/c8ra03799j. eCollection 2018 Aug 2.

C-H activation-annulation on the N-heterocyclic carbene platform

Champak Dutta  1 , Joyanta Choudhury  1
Affiliations
Review

C-H activation-annulation on the N-heterocyclic carbene platform

Champak Dutta et al. RSC Adv. .

Abstract

Ring-fused cationic N-heterocycles are an important class of organic compounds recognized to be of significant interest in diverse research areas including bioactivity, materials chemistry, supramolecular chemistry, etc. Toward the synthesis of such molecules, recently unique chemistry has been explored utilizing a novel conjugative action of NHC ligands as a functionalizable directing group in rhodium(iii)-catalyzed aromatic/heteroaromatic/non-aromatic C-H activation and subsequent annulation of various imidazolium salts with internal alkynes. This review highlights the initial development and underscores the potential of this chemistry.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1
Fig. 1. Scope for exploitation of reactivity in M–NHC motifs.
Fig. 2
Fig. 2. Strategy of C–H functionalization on M–NHC platform.
Scheme 1
Scheme 1. First report on catalytic transformation of Rh–NHC template.
Scheme 2
Scheme 2. Stoichiometric/catalytic C–H activation–functionalization directed by NHC.
Scheme 3
Scheme 3. Plausible mechanism for C–H annulation at non-chelating Rh–NHC platform.
Scheme 4
Scheme 4. C–H activation/annulation at 4-pyridyl-Rh–NHC template.
Scheme 5
Scheme 5. Plausible mechanism for NHC directed C–H activation/annulation of pyridyl C–H bond.
Scheme 6
Scheme 6. Cascade functionalization of Rh–nNHC and Rh–aNHC template.
Scheme 7
Scheme 7. Proposed mechanism for cascade C–H activation/annulation.
Scheme 8
Scheme 8. Wang's procedure of C–H activation-annulation at Rh–NHC platform.
Scheme 9
Scheme 9. Functionalizing Rh(iii)–NHC template for non-aromatic sp2 C–H activation.
Scheme 10
Scheme 10. Proposed mechanism for non-aromatic sp2 C–H activation/annulation.
Scheme 11
Scheme 11. Bimodal ‘rollover’ process at chelated Rh–NHC platform.
Scheme 12
Scheme 12. Steric and electronics induced stoichiometric rollover cyclometalation.
Scheme 13
Scheme 13. Rollover functionalization of Rh–NHC metallachelate.
Scheme 14
Scheme 14. Plausible mechanism for ‘rollover’ C–H annulation at Rh–NHC platform.
Scheme 15
Scheme 15. NHC rollover functionalization of Rh–NHC metallachelate.
Scheme 16
Scheme 16. Stereoelectronically biased C–H functionalization at Rh–aNHC platform.
Scheme 17
Scheme 17. Bimodal C–H activation/annulation at Rh–aNHC template.
Scheme 18
Scheme 18. Plausible mechanism for ‘rollover’ C–H annulation at Rh–aNHC platform.
Scheme 19
Scheme 19. Switching of reaction pathway from C–C rollover to C–N ring-extension annulation.
Fig. 3
Fig. 3. Images of selected synthesized annulated products under UV light.
None
Champak Dutta
None
Joyanta Choudhury
See this image and copyright information in PMC

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