21 不斉(2+2)光環化付加反応による抗腫瘍性ジテルペン、スパトールの不斉全合成へのアプローチ

概要

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The first total synthesis of antitumor diterpene spatol 1 is achieved in optically active form. The key step of this synthesis is the construction of tricyclo[5,3,0,0^<2.6>]decane nucleus. Intermolecular photocycloaddition of chiral butenolide 9 and olefin 10 gave the adduct 11 as a major product by the approach of 10 from the less hindered side. Transformation of the lactone ring of 11 into cyclopentenone ring gave 15, which was then successfully converted to β-bourbonene 3. For the construction of tricyclic nucleus of 1, the approach of 10 from the more hindered side of 9 is necessary, but was not the main course of the above intermolecular cycloaddition reaction. However this approach was realized by the intramolecular version of this cycloaddition. Thus, irradiation of 28 gave 29 and 30, having requisite configurations and functionalities. 29 and 30 were elaborated to 42, which possesses the common structure of all spatane diterpenes. Conversion of 42 into stoechospermol 2 was achieved by introducing the prenyl moiety to 42. Finally, conversion of 42 into sulfonium salt 45, generation of sulfur ylide, and addition to optically active aldehyde 47 gave the objective spatane diterpene (+)-spatol 1 in optically pure form having natural configuration.
1985-09-07