- Progress towards viridin: Synthesis of the pentacyclic furanosteroid ring system via o-benzoquinonoid cycloadditions
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The pentacyclic ring system of viridin is synthesised in nine steps from 4-methylguaicol by means of successive cycloadditions involving o-benzoquinonoid intermediates generated in situ.
- Souza, Fabio E. S.,Rodrigo, Russell
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p. 1947 - 1948
(2007/10/03)
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- Quassinoid Synthesis via o-Quinone Diels-Alder Reactions
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The reaction of 3,5-disubstituted o-quinones (2a, 2c) and 4-chloro-3,5-disubstituted o-quinones (2b, 2d) with simple dienes was investigated as a potential route to the quassinoid skeleton.Quinones 2a and 2c reacted in high yield at the 3,4-position with only a small excess of diene.Attempted equilibration of cis-fused cycloadducts to the trans-fused system failed due to the intervention of a stable enol form, as in 20.Compound 2c with ethyl 3,5-hexadienoate gave 15a, which upon reduction and lactonization provided BCD-ring tricyclic quassinoid analogues 18a and 19a.Again isomerization to the BC trans-fused system was not possible.The chloroquinones showed some preference for Diels-Alder reaction at the 5,6-position, but the additions were characterized generelly by low yields, side reactions, and lessened stereoselectivity.
- Weller, Dwight D.,Stirchak, Eugene P.
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p. 4873 - 4879
(2007/10/02)
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