21 抗腫瘍性セスキテルペン,ヴェルノレピンおよびヴェルノメニンの全合成

抄録

The total synthesis of dl-vernolepin and vernomenin, tumor inhibiting sesqueterpene lactone, was achieved by the following route. Novel highly active diene 4 was prepared and it was proved that Diels-Alder reaction of 4 with some proper dienophiles involved new sythetic route to Δ^1-octalin-3-one systems. This procedure was applied to the stereospecific synthesis of the key intermediate, protected epoxide 53. Diels-Alder adduct 20 was converted to the epoxydilactone 29, which on unusual orthoesterification gave orthoester 40. DIBAH reduction of 40, followed by Wittig reaction yielded 53. The remarkable epoxide opening by the action of dilithioacetate on 53 with inversion at C_7 position, followed by cyclization afforded precursors 57, 58, which were transformed to vernolepin and vernomenin by novel method of bis-α-methylenation. The synthesis was achieved in 18 steps and 1.6% overall yield.