Selective oxidation of thiacalix[4]arene (cone) to all corresponding sulfoxides
Graphical abstract
Introduction
Thiacalix[4]arene 1 emerged1 as a novel member of the calix[n]arene2 family two decades ago, and since then, this molecule has attracted considerable attention as a potential candidate for use as a novel building block and molecular scaffold. As recently reviewed,3 the introduction of sulfur atoms (instead of CH2 groups) has a dramatic consequence on the complexation ability, amended conformational behavior and even substantially different chemistry compared with that of the classical (methylene-bridged) calixarenes. Consequently, some reactions which are virtually unknown and/or impossible in the chemistry of calix[4]arene have been reported for thiacalix[4]arenes, such as regio- and stereo-selective S-alkylation to form sulfonium salts,4 or chemoselective S-oxidation to provide various sulfoxides or sulfones (Fig. 1).5
Thus, the extensive oxidation of parent thiacalixarene 1 (H2O2/TFA or NaBO3/CHCl3–AcOH) provides the corresponding tetrasulfone derivative 3 whereas an equivalent amount of oxidizing agent (NaBO3) gives tetrasulfoxide 2.6 While the oxidation of all bridging sulfur atoms in lower rim-unsubstituted or substituted7 thiacalix[4]arenes is well documented, regioselective partial oxidation of the individual bridges is still rare in the literature. In fact, only two compounds, thiacalix[4]arene fixed in the cone conformation by four benzyl2(b), 8 or ethyl acetate9 groups, both possessing the tert-butyl groups on the upper rim, have been reported so far for selective partial oxidation. As the chemical and/or conformational behavior of thiacalixarene systems could be dramatically dependent on the upper rim substitution we postulated that the upper rim-unsubstituted thiacalix[4]arenes could also be selectively oxidized. In this Letter we report the regioselective oxidation of tetrapropoxythiacalix[4]arene 4, immobilized in the cone conformation, leading to the formation of all possible sulfinyl derivatives. Based on dynamic NMR studies, these products show an interesting relationship between the number of sulfinyl groups and the conformational behavior of the macrocycles.
Section snippets
Results and discussion
Starting tetrapropoxythiacalixarene 4 (cone) was oxidized using various oxidizing agents. Thus, treatment with PCC provided monosulfinyl derivative 5 in acceptable yields, on the other hand, the same reagent used in excess (up to 40 equiv) always yielded a mixture of mono- and di-sulfinyl compounds 5–7 in various ratios. Similar reactivity was observed for 35% aqueous H2O2 in AcOH, again leading only to the less oxidized derivatives. The application of 100% HNO3 in AcOH (successfully used for
Acknowledgment
This research was supported by the Czech Science Foundation (15-17572S).
References and notes (20)
- et al.
Tetrahedron Lett.
(1997) - et al.
J. Chem. Soc., Perkin Trans. 2
(2002) - et al.
J. Appl. Cryst.
(2003) - et al.
J. Appl. Cryst.
(2007) APEX3, SAINT
(2015)Calixarenes an Introduction
(2008)Calixarenes Revisited
et al.Calixarenes in Action
(2000)- et al.
Chem. Soc. Rev.
(2014)et al.Chem. Rev.
(2006)Eur. J. Org. Chem.
(2004) - et al.
Org. Lett.
(2011)et al.J. Org. Chem.
(2012)
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