Reduction of 4-azidonaphthalimide with different phosphine ligands and exploration of their spectroscopic properties
Graphical abstract
Introduction
Recently, 4-amino-1,8-naphthalimides (1) have emerged as an important class of organic fluorophores [1] as a consequence its wide applications in DNA targeting binders [2], fluorescent sensors [3], fluorescent cellular imaging agents [4] and supramolecular chemistry [5]. Up to now, 4-amino-1,8-naphthalimides are usually synthesized by several methods including: (i) the reduction of the 4-nitro-1,8-naphthalimides with SnCl2/HCl [6]; (iii) substitution of the 4-bromo-1,8-naphthalimides with conc. ammonia and copper power [7]; (iii) the reduction of the 4-azide-1,8-naphthalimides with H2S [8]. Generally, the drawbacks of these methods are low-yield, or transition-metal catalyzed, even using harmful gas. The formation of primary amines is a cornerstone of organic synthesis. The reduction of azides is commonly achieved through the Staudinger procedure using PPh3. In this regard, we recently attempted to form compound 1 from the 4-azidonaphthalimide compound (4) using PPh3. However, we found the reduction of the azide 4 to iminophosphorane 2 rather than the formation of the desired amine 1. Wondrously, the desired amine 1 was obtained with PPh3 being replaced by PMe3 in high yield at room temperature. With this transformation in mind, several 4-substituted 1,8-naphthalimide and 1,8-Naphthalic anhydride derivatives have been designed and synthesized to investigate the reduction of the azide compounds 4 and 7 with different phosphine ligands including PPh3, PMe3, bis(1,3-diphenylphosphino)propane (dppp), and 1,1′-Bis(diphenylphosphino)ferrocene (dppf) in the paper. As far as we know, a few studies on the photophysical properties of iminophosphorane-naphthalimides have been reported. Therefore, the electronic spectroscopy behavior of the corresponding reduction products has been also investigated.
Section snippets
General procedures
All manipulations were carried out at room temperature under a nitrogen atmosphere using standard Schlenk techniques, unless otherwise stated. All reagents were purchased from commercial sources and were used without further purification. 1H, 13C, and 31P NMR spectra were collected on a Bruker 500 MHz magnetic resonance spectrometer. 1H and 13C NMR chemical shifts are relative to TMS, and 31P NMR chemical shifts are relative to 85% H3PO4. Mass spectrometry was recorded with a Bruker amaZon SL
Synthesis
Reduction of 4- azido-1,8-naphthalimide with different phosphine ligands is shown in Scheme 1. Initially, the iminophosphorane 2 was obtained after the reduction of 4-azidonaphthalimide compound (4) using PPh3 in 40% yield. Unfortunately, only 5% hydrolyzation to the amine 1 was observed (Scheme 1). With this transformation in mind, we attempted to use the phosphine ligand PMe3. Wondrously, the desired amine 1 was obtained in 93% yield. In the next moment, the corresponding iminophosphorane 3
Conclusion
In summary, several 4-substituted 1,8-naphthalimide and 1,8-Naphthalic anhydride iminophosphoranes were successfully synthesized from the reduction of the corresponding azides with different phosphine ligands. Notably, we developed a convenient, high efficient method for the reduction of 4-azidonaphthalimide to 4-aminonaphthalimide by using PMe3. Optical studies indicated the introduction of the different phosphine ligands have large effects on their optical properties, which make them which
Acknowledgments
The authors acknowledge financial support from National Natural Science Foundation of China (Nos. 21002086), and the Natural Science Foundation of Yunnan Province (No. 2010ZC071).
References (14)
- et al.
Dyes Pigments
(2002)et al.Dyes Pigments
(1993)et al.Dyes Pigments
(1985)et al.J. Phys. Chem. C
(2009) - et al.
J. Org. Chem.
(2010)et al.Chem. Commun.
(2013)et al.Eur. J. Med. Chem.
(2013)et al.J. Org. Chem.
(2014)et al.Org. Lett.
(2009) - et al.
J. Org. Chem.
(2006)et al.Org. Lett.
(2005)et al.Dyes Pigments
(2015) - et al.
Org. Biomol. Chem.
(2013) - et al.
Z. Naturforsch B
(1988) - et al.
J. Am. Chem. Soc.
(2012)et al.J. Am. Chem. Soc.
(2012)et al.Chem. Commun.
(2010)et al.Tetrahedron Lett.
(2009)et al.J. Org. Chem.
(2014)et al.J. Am. Chem. Soc.
(2008) - et al.
J. Org. Chem.
(2008)et al.Org. Biomol. Chem.
(2009)et al.J. Org. Chem.
(2005)