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Science 14 April 2006:
Vol. 312. no. 5771, pp. 251 - 254
DOI: 10.1126/science.1124985
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Reports

Diels-Alder in Aqueous Molecular Hosts: Unusual Regioselectivity and Efficient Catalysis

Michito Yoshizawa, Masazumi Tamura, Makoto Fujita*

Self-assembled, hollow molecular structures are appealing as synthetic hosts for mediating chemical reactions. However, product binding has inhibited catalytic turnover in such systems, and selectivity has rarely approached the levels observed in more structurally elaborate natural enzymes. We found that an aqueous organopalladium cage induces highly unusual regioselectivity in the Diels-Alder coupling of anthracene and phthalimide guests, promoting reaction at a terminal rather than central anthracene ring. Moreover, a similar bowl-shaped host attains efficient catalytic turnover in coupling the same substrates (although with the conventional regiochemistry), most likely because the product geometry inhibits the aromatic stacking interactions that attract the planar reagents to the host.

Department of Applied Chemistry, School of Engineering, University of Tokyo, and Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.

* To whom correspondence should be addressed. E-mail: mfujita{at}appchem.t.u-tokyo.ac.jp

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