Issue 7, 2021

Molecular engineering enabling reversible transformation between helical and planar conformations by cyclization of alkynes

Abstract

Molecular engineering enabling reversible transformation between helical and planar conformations is described herein. Starting from easily available 2-(pyridin-2-yl)anilines and alkynes, a one-pot strategy is set up for the synthesis of aza[4]helicenes via two successive rhodium-catalyzed C–H activation/cyclizations. Helical pyrrolophenanthridiziniums can be transformed into planar conformations through the cleavage of acidic pyrrole N–H, leading to turn-off fluorescence. NMR spectra, single crystal X-ray diffraction and DFT calculations demonstrate that the formation of an intramolecular C–H⋯N hydrogen bond is beneficial to stabilize the pyrrole nitrogen anion of the planar molecule and provide increased planarity. The reversible conformation transformations can be finely adjusted by the electron-donating and -withdrawing groups on the π+-fused pyrrole skeleton in the physiological pH range, thus affording an opportunity for pH-controlled intracellular selective fluorescence imaging. Pyrrolophenanthridiziniums show turn-on fluorescence in lysosomes owing to the acidic environment of lysosomes and turn-off fluorescence out of lysosomes, indicating the occurrence of the deprotonation reaction outside lysosomes and the corresponding transformation from helical to planar conformations.

Graphical abstract: Molecular engineering enabling reversible transformation between helical and planar conformations by cyclization of alkynes

Supplementary files

Article information

Article type
Edge Article
Submitted
23 okt 2020
Accepted
03 dec 2020
First published
08 dec 2020
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2021,12, 2419-2426

Molecular engineering enabling reversible transformation between helical and planar conformations by cyclization of alkynes

L. Yan, W. Ma, J. Lan, H. Cheng, Z. Bin, D. Wu and J. You, Chem. Sci., 2021, 12, 2419 DOI: 10.1039/D0SC05844K

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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