Abstract
The chemoselective reaction of the C- followed by the O-centered naphthyl radicals with the more electron-deficient hypervalent bond of the diaryliodonium(III) salts is described. This discovered reactivity constitutes a new activation mode of the diaryliodonium(III) salts which enabled a one-pot doubly arylation of naphthols through the sequential -/O- bond formation. The naphthyl radicals were generated in the reaction by the tetramethylpiperidinyl radical (TMP·) which resulted from the homolytic fragmentation of the precursor TMP2O. Experimental and DFT calculations provided a complete panorama of the reaction mechanism.
Highlights
The chemistry of radicals is a powerful tool in organic synthesis allowing chemical transformations with high activation energy profiles via HAT (Capaldo and Ravelli, 2017), SET (Kita et al, 1994, 1996; Rosen and Percec, 2009) or SOMO (Beesson et al, 2007)
In the course of this work, we fortuitously discovered and later synthesized the new radical precursor TMP2O [1,1′-oxybis(2,2,6,6-tetramethylpiperidine)] which, according to our DFT calculations, spontaneously undergoes homolytic fragmentation leading to the formation of the TEMPO and tetramethylpiperidinyl (TMP·) radicals
High-resolution masses (HRMS) analyses were obtained under the following procedure: Samples were introduced by direct infusion at 3 μL min−1 to the electrospray ionization (ESI) source of a quadrupole time-of-flight mass spectrometer (Bruker Daltonics ESI-QTOFMS maXis impact), equipped with Data Analysis 4.1
Summary
The chemistry of radicals is a powerful tool in organic synthesis allowing chemical transformations with high activation energy profiles via HAT (Capaldo and Ravelli, 2017), SET (Kita et al, 1994, 1996; Rosen and Percec, 2009) or SOMO (Beesson et al, 2007) Both C- and O-centered radical formation on the naphthol moiety are known processes carried out by metals such as Cu (Nakajima et al, 1999; Li et al, 2001), Ru (Irie et al, 2000), Fe (Egami and Katsuki, 2009; Narute et al, 2016), Cr (Nieves-Quinones et al, 2019), or V (Brodwel and Cheng, 1991; Hon et al, 2001; Lee et al, 2014; Kang et al, 2017). Both radical and Ar2IX strategies (Moteki et al, 2013; Wang and Studer, 2017; Ye et al, 2018) have been used in the preparation of aryl phenols which are important synthetic targets due to their relevance as biologically active molecules (Zofou et al, 2013; Ramadoss et al, 2016, 2018a,b, 2019; Gutierrez-Cano et al, 2017), reagents (Grzybowski et al, 2013), building blocks (Dreher et al, 2000), and organocatalyst scaffolds (Parmar et al, 2014).
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