title: Synthetic studies towards the mulberry Diels-Alder adducts: H-bond accelerated cycloadditions of chalcones.
abstract: The methyl ether derivatives 2, 4 and 6 of the mulberry Diels-Alder adducts chalcomoracin (1) and mulberrofuran C (3) and kuwanon J (5) respectively have been synthesized by a thermal [4 + 2]-cycloaddition reaction between a chalcone and dehydroprenyl diene. A H-bonded ortho OH substituent on the chalcone was found to be essential for Diels-Alder reactivity. Density functional theory calculations show that the OH group lowers the barrier for the Diels-Alder reaction by 2-3 kcal mol(-1) compared with OMe. The acceleration by the OH group is traced to two transition-state effects: a stronger diene-chalcone interaction and better planarity of the aryl-diene unit.
authors.affiliation: School of Chemistry, The Bio21 Institute, The University of Melbourne, VIC 3010, Australia.
authors.forename: Sompong
authors.initials: S
authors.lastname: Boonsri
authors.forename: Christian
authors.initials: C
authors.lastname: Gunawan
authors.forename: Elizabeth H
authors.initials: EH
authors.lastname: Krenske
authors.forename: Mark A
authors.initials: MA
authors.lastname: Rizzacasa
mesh_terms: D047188:Chalcones / Q000138:chemical synthesis* / Q000737:chemistry*; D060326:Chemistry Techniques, Synthetic; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008968:Molecular Conformation; D031625:Morus / Q000737:chemistry*
chemical_list: D047188:Chalcones