of rare natural polyphenols biosynthetically derived from [4 + 2]-cycloaddition of chalcones and dehydroprenylphenols. In this study, kuwanons G (1) and H (2), two bioactive MDAAs with unique dehydroprenylflavonoid dienes, were totally synthesized for the first time in a biomimetic manner. The key features of the convergent route include the use of the Baker–Venkataraman rearrangement, alkylation of
copper(I)-catalyzed vinylation of diazo compounds with vinylbenziodoxolone reagents (VBX) as partners is reported. The transformation tolerates diversefunctionalities on both reagents delivering polyfunctionalized vinylated products. The strategy was successfully extended to a three-component/intermolecular version with alcohols. The obtained products contain synthetically versatile functional groups, such
Radical-polar crossover reactions of dienylboronate complexes are applied to the synthesis of functionalized secondary and tertiary allylboronic esters. The transition-metal-free three-component couplinguses readily accessible dienylboronate esters as substrates in combination with various sp3/sp2 carbon nucleophiles and commercial alkyliodides as radical precursors. In the visible light-initiated
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.