690233-34-2Relevant articles and documents
A novel synthesis of 2-alkoxy-3-hydroxytropones and 2,7-dihydroxytropones from dialkoxy-8-oxabicyclo[3.2.1]oct-6-en-3-ones
Zinser, Hartmut,Henkel, Sonja,Foehlisch, Baldur
, p. 1344 - 1356 (2007/10/03)
Trichloro-substituted 8-oxabicyclo[3.2.1]oct-6-en-3-ones 6 and 7 are solvolysed by methanolic sodium methoxide to form the bicyclo[3.2.1] α,α-dimethoxy ketones 13 and 14, with preservation of one chloro substituent. In the case of 6a, prolonged reaction time with an excess of methanolic sodium methoxide provides a trimethoxy-substituted oxanorbornene aldehyde 19 through ring contraction. Treatment of the mixture of 13 and 14 with zinc and aqueous acetic acid affords dechlorinated α-oxo acetals 15 and 16. Starting with the [4+3] cycloadducts derived from 2-methylfuran and tetrachloroacetones (6b and 7b), the same procedure, but with use of ethanol or trifluoroethanol, results in the corresponding ethoxy- and trifluoroethoxy acetals. These compounds can be converted into the oxabicyclic compounds 15, which undergo cleavage of the ether bridge on heating with KOH in methanol, thus providing 2-alkoxy-3-hydroxytropones 20, which can be dealkylated to give the 2,7-dihydroxytropones (7-hydroxytropolones) 29. The lithium enolate generated from the α-oxo acetal 15a can be exo-alkylated with methyl iodide. Michael addition with 2-nitro-1-butene followed by a Nef reaction furnishes the bicyclic dioxo acetal 5. Treatment of 5 with basic methanol results in an epoxyazulenone derivative 26, and a hydroxytropone 20f, which is in equilibrium with the cyclic hemiacetal form 28. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
