New rearrangement reactions of the trichothecane framework]

Treatment of the apotrichothecane derivative 4 with H₂SO₄ in dioxan gave the acetal 6 and with H₂SO₄ in acetone the ketal 9 . Whereas the oxidation of 4 with Ag₂CO₃ yielded the hydroxy aldehyde 7 , the reaction with CrO₃ or MnO₂ led to the α,β-unsaturated ketone 8 . Upon treatment of 8 with base the cyclic keto ether 11 was obtained due to 1,4-addition. Acetylation of the latter compound gave a mixture consisting of the enolacetate 13 and the acetylketone 14 . The oxim 15 of ketone 14 was transformed to the nitrile 16 and not the Beckmann fragmentation product 18 . For the identification of the C(11) hydrogen atom in biosynthetic studies the triol 22 was oxidized to the keto aldehyde 26 which, upon treatment with methanolic K₂CO₃, gave the spirolactol 30 and the cyclic acetal 29 as second product when the reaction was carried out in dilute solution. The spirolactol 30 was oxidized to the spirolactone 31 . The corresponding 19 possessing the intact 12,13-epoxy group underwent rearrangement to the apotrichothecane derivatives 20 and 21 under the same conditions. Oxidation of the triol 22 with MnO₂ or CrO₃ gave a mixture of the acetal 23 and the keto acid 24 . – The mechanisms of the rearrangements observed are discussed.