A seven-step synthesis of the sesquiterpene dihydrocostunolide (1) from santonin (5) is described. The key elements of this approach, the first to yield a synthetic sesquiterpene in the cyclodecadiene series, are the photolytic cleavage of the hexahydronaphthalene derivative 10 to form a cyclodecatriene (13) and the subsequent selective hydrogenation to a cyclodeca-1,5-diene (1).

comparison with authentic 4-acetoxyacetanilide indicated that no detectable amount of this compound was formed in the reaction.

was found that, if instead a large excess of NaNs (>2.1 equiv) is used, then complete conversion of 2a to 3a and further conversion of 3a to 4a could be effected almost completely at room temperature without requiring the use of any other base. However, the method, as a direct route from 2a-f to 4a-f necessitated long reaction times for complete conversion, and thus an alternate procedure (Scheme I) was developed whereby

4829ents,I7 one of them again being Na in liquid NH3.I8 In fact treatment of 6 with this reagent furnishes 4 in 32% yield. 16 Hydrocarbon 4, isolated as a colorless solid (mp 27-30 "C) by preparative GLC on SE 30 at 50 O C , is characterized by its mass spectrum (very similar to that of cubane") [ m / e 104 (15), 103

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