Synthèse des (±)‐loliolide, (±)‐actinidiolide, (±)‐dihydroactinidiolide et dérivés à partir d'acide homosafranique. Photooxygénation sensibilisée de I'homosafranate de méthyle

We have synthesized (±)‐loliolide ( 7 a ), (±)‐actinidiolide ( 11 a ), (±)‐dihydroactinidiolide ( 16 ), and (±)‐isodihydroactinidiolide ( 18 ) through various reaction paths starting from homosafranic acid ( 4 a ). Thus, (±)‐actinidiolide has been synthesized for the first time, and this result allows to discard the alternative formula 11 b for that compound [2]. By investigation of the sensitized photooxygenation of methyl homosafranate ( 4 b ), this reaction is shown to lead to an interesting spiro‐peroxylactone 25 , beside the expected endo ‐peroxide 23 . Specific oxygenation of the tetrasubstituted double bond of methyl homosafranate, and cyclisation of the hydroperoxide 24 thus produced, are believed to account for the formation of such a particular compound. The base‐catalysed rearrangement of the endo ‐peroxide 23 gives rise to two compounds, one being the expected keto‐hydroxy‐ester 26 . The other ‐ to which is assigned the glycidic ester structure 27 ‐ obviously results from an internal displacement reaction on oxygen in 23 . It is note‐worthy that the sensitized photooxygenation of methyl homosafranate proceeds directly to the same glycidic ester when it is carried out in an alcaline solution.