The totalsynthesis of the Diels–Alder-type adducts (±)-kuwanol E and the heptamethyl ether derivative of (±)-kuwanon Y has been accomplished via a convergent strategy involving 2′-hydroxychalcone 6 or 9 and dehydroprenylstilbene 7, in nine steps. The synthesis features, as a key step, a Lewis acid-mediated biomimetic intermolecular Diels–Alder [4+2] cycloaddition for the construction of the cyclohexene
Synthetic studies towards the mulberry Diels–Alder adducts: H-bond accelerated cycloadditions of chalcones
作者:Sompong Boonsri、Christian Gunawan、Elizabeth H. Krenske、Mark A. Rizzacasa
DOI:10.1039/c2ob25115a
日期:——
The methyl ether derivatives 2, 4 and 6 of the mulberry DielsâAlder 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 DielsâAlder reactivity. Density functional theory calculations show that the OH group lowers the barrier for the DielsâAlder reaction by 2â3 kcal molâ1 compared with OMe. The acceleration by the OH group is traced to two transition-state effects: a stronger dieneâchalcone interaction and better planarity of the arylâdiene unit.
Biosynthesis of optically active Diels–Alder type adducts revealed by an aberrant metabolism of O-methylated precursors in Morus alba cell cultures
作者:Yoshio Hano、Taro Nomura、Shinichi Ueda
DOI:10.1039/c39900000610
日期:——
Addition of O-methylated chalcone, as precursors, to Morusalbacellcultures has resulted in the formation of opticallyactive O-methyl derivatives of chalcomoracin (1) and kuwanon J (2), corroborating the pivotal step of the biosynthesis of (1) and (2) to be the enzymic Diels–Alder reaction.