Intramolecular Diels-Alder Reactions Platencin Banwell , Platensimycin Matsuo , - -Halenaquinone Trauner , -Cassaine Deslongchamps

New approaches to the intramolecular Diels-Alder reaction continue to be introduced. Mathias Christmann, now at the TU Dortmund, showed (Angew. Chem. Int. Ed. 2008, 47, 1450) that a secondary amine organocatalyst converted the prochiral dialdehyde 19 into the hicycHc diene 20 with high de and ee. Martin G. Banwell of the Australian National University prepared Organic Lett. 2008,10,4465) the triene 21 in high ee by microbiological oxidation of iodobenzene. On warming, 21 was converted smoothly into 22, which was carried on in a formal synthesis of platencin. 

Benjamin List of the Max Planck Institute, MiiUieim devised J. Am. Chem. Soc. 2008,130, 6070) a chiral primary amine salt that catalyzed the enantioselective epoxidation of cyclo-hexenone 1. Larger ring and alkyl-substituted enones are also epoxidized with high ee. 

Three- and four-membered rings are versatile intermediates for further transformation. Tsutomu Katsuki of Kyushu University developed Angew. Chem. Int. Ed. 2008, 47, 2450) an elegant Al(salalen) catalyst for the enantioselective Simmons-Smith cyclopropanation of allylic alcohols such as 3. Kazuaki Ishihara of Nagoya University found J. Am. Chem. Soc. 2007,129, 8930) chiral amine salts that effected enantioselective 2-1-2 cycloaddition of a-acyloxyacroleins such as 5 to alkenes to give the cyclobutane 7 with high enantio- and diastereocontrol. 

Tony K. M. Shing of the Chinese University of Hong Kong devised J. Org. Chem. 2007, 72, 6610) a simple protocol for the conversion of carbohydrate-derived lactones such as 19 to the highly-substituted, enantiomerically-pure cyclohexenone 21. Hiromichi Fujioka and Yasuyuki Kita of Osaka University established Organic Lett. 2007, 9, 5605) a chiral diol-mediated conversion of the cyclohexadiene 22 to the diastereomericaUy pure cyclohexenone 24. 

Dirk Trauner, now of the University of Munich, reported (Organic Lett. 2008,10, 149) an elegant assembly of the neuritogenic polyketide shimalactone A 28. As anticipated, the polyene prepared by StiUe coupling of the iodide 25 with the stannane 26 underwent 8 n cyclization to 27, that then spontaneously imderwent 8 7i cyclization to 28, with substantial diastereocontrol. 

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Intermolecular and Intramolecular DIels-Alder Reactions Platencin (Banwell), Platensimycin (Matsuo), (-)-Halenaquinone (Trauner), (+)-Cassaine (Deslongchamps)... 

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