Templating Photodimerization of trans-Cinnamic Acids with Cucurbit[8]uril and γ-Cyclodextrin Mahesh Pattabiraman, Arunkumar Natarajan, Lakshmi S. Kaanumalle, and V. Ramamurthy* Department of Chemistry, Tulane UniVersity, New Orleans, Louisiana 70118 murthy@tulane.edu Received October 15, 2004 (Revised Manuscript Received December 29, 2004) ABSTRACT Cucurbit[8]uril and γ-cyclodextrin are able to align two olefin molecules in a head-head fashion within their large cavities. Excitation of such templated olefins results in syn head-head cyclobutanes in nearly quantitative yields. The methodology revealed here works with trans- cinnamic acids that do not dimerize either in solution or in the solid state and with the ones that yield only anti head-tail dimer in the solid state. The reactions of trans-cinnamic acids are examples of [2 + 2] photodimerization that have been investigated extensively since 1889. 1 Some of these acids exhibit a dual behavior on photolysis dependent on the reaction medium. While in solution trans-cis isomerization occurs exclusively, on photolysis of the crystal these acids react to give dimeric products under conditions where the two reactive CdC bonds are within the topochemically stipulated distance (<4.2 Å) and parallel (Scheme 1). 2,3 Most of the current efforts in solid-state photochemistry are devoted to establishing reliable strategies that would steer molecules so as to obtain a crystal structure that would favor photodimerization. 4 In this paper, we establish the utility of cucurbit[8]uril (CB[8]) 5 and γ-cyclodextrin (γ-CD) in templating photodimerization of a variety of trans-cinnamic acids to a single isomer (syn head- head dimer) both in solution and the solid state. Remarkably, the methodology reported here with CB[8] and γ-CD is general and works with a number of cinnamic acids that do not dimerize (γ-packing) and also with the ones that give anti head-tail dimers (R-packing) in solid state. Since CB[8] is known to include mostly cationic guest molecules, until now its scope as a reaction medium has been limited. Photodimerization of C 2 -symmetric trans-diaminostilbene hydrochloride within CB[8] has recently been reported. 6 As far as we are aware, neither neutral olefins nor olefins with different substituents have been included and aligned within CB[8]. We show in this report that CB[8] can include neutral (1) (a) Liebermann, C. Chem. Ber. 1989, 122, 124. (b) Liebermann, C. Chem. Ber. 1989, 122, 782. (2) (a) Cohen, M. D.; Schmidt, G. M. J. J. Chem. Soc. 1964, 1996. (b) Cohen, M. D.; Schmidt, G. M. J. J. Chem. Soc. 1964, 2000. (c) Schmidt, G. M. J. J. Chem. Soc. 1964, 2014. (3) Ramamurthy, V.; Venkatesan, K. Chem. ReV. 1987, 87, 433. (4) (a) Toda, F. Acc. Chem. Res. 1995, 28, 480. (b) Ito, Y.; Kitada, T.; Horiguchi, M. Tetrahedron 2003, 59, 7323. (c) Ito, Y.; Borecka, B.; Totter, J.; Scheffer, J. R. Tetrahedron Lett. 1995, 36, 6083. (d) MacGillivray, L. R.; Reid, J. L.; Ripmeester, J. A. J. Am. Chem. Soc. 2000, 122, 7817. (e) Gao, X.; Friscic, T.; MacGillivray, L. R. Angew. Chem., Int. Ed. 2003, 43, 232. (f) Papaefstahiou, G. S.; Zhong, Z.; Geng, L.; MacGillivray, L. R. J. Am. Chem. Soc. 2004, 126, 9158. (g) Caronna, T.; Liantonio, R.; Logothetis, T. A.; Metrangolo, P.; Pilati, T.; Resnati, G. J. Am. Chem. Soc. 2004, 126, 4500. (h) Shan, N.; Jones, W. Tetrahedron Lett. 2003, 44, 3687. (5) (a) Mock, W. L. Top. Curr. Chem. 1995, 175, 1. (b) Day, A.; Arnold, A. P.; Blanch, R. J.; Sunshall, B. J. Org. Chem. 2001, 66, 8094. (c) Kim, J.; Jung, I.-S.; Kim, S.-Y.; Lee, E.; Kang, J.-K.; Sakamoto, S.; Yamaguchi, K.; Kim, K. J. Am. Chem. Soc. 2000, 122, 540. ORGANIC LETTERS 2005 Vol. 7, No. 4 529-532 10.1021/ol047866k CCC: $30.25 © 2005 American Chemical Society Published on Web 01/21/2005