Unusual Intramolecular Bridging Reaction in Thiacalix[4]arene Series Ondrej Kundrat, † Hana Dvorakova, § Ivana Cisarova, ‡ Michaela Pojarova, † and Pavel Lhotak* ,† Department of Organic Chemistry and Laboratory of NMR Spectroscopy, Prague Institute of Chemical Technology, Technicka 6, 166 28 Prague 6, Czech Republic, and Department of Inorganic Chemistry, Charles UniVersity, HlaVoVa 8, 128 43 Prague 2, Czech Republic lhotakp@Vscht.cz Received August 5, 2009 ABSTRACT Thiacalix[4]arene immobilized in the cone conformation undergoes a direct formylation reaction giving unusual products in high yields. The Duff reaction (urotropine/TFA) leads to unprecedented intramolecularly bridged compounds possessing two formyl groups on the opposite para- or para-/meta-positions. The comparison with the corresponding classical calix[4]arene analogues indicates an amazingly different reactivity of the thiacalix[4]arene system. Since their first appearance in 1997, thiacalix[4]arenes 1 have received considerable attention from the supramolecular community. Incorporation of four sulfur atoms instead of the common methylene bridges imparts many novel features to the thiacalix[4]arene derivatives 2 when compared to the classical analogues. Thiacalix[4]arenes exhibit substantially enhanced complexation capacities for transition metals, 3 considerably different conformational behaviors/preferences, 4 and novel types of chemistry 5 (e.g., oxidation of sulfur bridges) to mention at least some of their novel functions. All these features make them very promising candidates for the role of host molecules and/or building blocks with many potential applications in supramolecular chemistry. On the other hand, despite more than a decade of research on thiacalixarenes, our knowledge of their chemistry is still rather fragmented. Consequently, the broader application of † Department of Organic Chemistry, Prague Institute of Chemical Technology. ‡ Laboratory of NMR Spectroscopy, Prague Institute of Chemical Technology. § Department of Inorganic Chemistry, Charles University. (1) Kumagai, H.; Hasegawa, M.; Miyanari, S.; Sugawa, Y.; Sato, Y.; Hori, T.; Ueda, S.; Kamiyama, H.; Miyano, S. Tetrahedron Lett. 1997, 38, 3971. (2) For recent reviews on thiacalixarenes, see: (a) Morohashi, N.; Narumi, F.; Iki, N.; Hattori, T.; Miyano, S. Chem. ReV. 2006, 106, 5291. (b) Lhotak, P. Eur. J. Org. Chem. 2004, 1675. (3) (a) Kajiwara, T.; Iki, N.; Yamashita, M. Coord. Chem. ReV. 2007, 251, 1734. (b) Morohashi, N.; Iki, N.; Sugawara, A.; Miyano, S. Tetrahedron 2001, 57, 5557. (c) Iki, N.; Morohashi, N.; Narumi, F.; Miyano, S. Bull. Chem. Soc. Jpn. 1998, 71, 1597. (4) (a) Lang, J.; Dvorakova ´, H.; Bartosova ´, I.; Lhota ´k, P.; Stibor, I.; Hrabal, R. Tetrahedron Lett. 1999, 40, 373. (b) Lang, J.; Vlach, J.; Dvorakova ´, H.; Lhota ´k, P.; Himl, M.; Hrabal, R.; Stibor, I. J. Chem. Soc., Perkin Trans. 2 2001, 576. (c) Cajan, M.; Lhota ´k, P.; Lang, J.; Dvorakova ´, H.; Stibor, I.; Koca, J. J. Chem. Soc., Perkin Trans. 2 2002, 1922. (d) Dvorakova ´, H.; Lang, J.; Vlach, J.; Sykora, J.; Cajan, M.; Himl, M.; Pojarova ´, M.; Stibor, I.; Lhota ´k, P. J. Org. Chem. 2007, 72, 7157. (5) (a) Katagiri, H.; Hattori, T.; Morohashi, N.; Iki, N.; Miyano, S. J. Org. Chem. 2007, 72, 8327. (b) Lhota ´k, P.; Mora ´vek, J.; S ˇ mejkal, T.; Stibor, I.; Sy ´kora, J. Tetrahedron Lett. 2003, 44, 7333. (c) Lhota ´k, P. Tetrahedron 2001, 57, 4775. (d) Morohashi, N.; Iki, N.; Sugawara, A.; Miyano, S. Tetrahedron 2001, 57, 5557. ORGANIC LETTERS 2009 Vol. 11, No. 18 4188-4191 10.1021/ol901812m CCC: $40.75  2009 American Chemical Society Published on Web 08/25/2009