P-16 サマリウム(II)を用いるシクロペンタノン誘導体の新規合成法の開発とその応用による天然物合成(ポスター発表の部)
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Numerous efforts have been made to produce bicyclic cyclopentanones, not only in consideration of their abundance in nature, but also their usefulness as versatile synthetic building blocks. The sequential reductive coupling-Dieckmann condensation reaction has been found quite useful as a one-step process for effectively producing oxacyclopentanecarboxylates from α,β-unsatureted esters. Electrohydrodimerization and metal-induced cyclization of cinnamate derivatives are methods generally applied for this purpose but none has been shown to produce in an intramolecular manner bicyclic oxacyclopentanecarboxylate. The authors have established two types of Sm12-induced sequential reaction to produce bicyclic cyclopentanones: 1) a sequential reductive cyclization-Dieckmann condensation of bis-α,β-unsaturated esters i with Sm-SmI_2 in the presence of catalytic amount of methanol to provide cyclopentanone ii (n=1, 2) (Scheme 2); and 2) a ring expansion reaction of 1,2-cyclobutanedicarboxylate iii with SmI_2-HMPA to provide ii (n=1 to 4) (Scheme 3), both of which involve iv and v as intermediates. The results of reactions of bis-α,β-unsaturated esters 1-4 with SmI_2 and 1,2-cyclobutanedicarboxylate 11-14 with SmI_2-HMPA are summarized in Table1 and Table 2, respectively. To show the synthetic utility of these reactions, we choose hirsutene as a synthetic target, which is typical member of triquinane sesquiterpene. And we wish to describe a new synthetic route to (±)-hirsutene, which involves SmI_2-induced sequential reactions, 3 to 6 and 23 to 25, as key steps (Scheme 5). (±)-1-Desoxyhypnophilin was also synthesized from common precursor 6 via rapid transformation of 6 into triquinane ring system 19 and reductive conversion of 19 into 21 (Scheme 4).
- 天然有機化合物討論会の論文
- 2007-08-24
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