A Formal Total Synthesis of Eleman-8β,12-olide with SmI₂-Induced Cyclization

Abstract

The formal total synthesis of elemane-type sesquiterpenoid eleman-8β,12-olide was conducted with samarium(II) iodide-induced cyclization as the key step.

Key words

eleman-8β,12-olide - enantioselective synthesis - sesquiterpenoid - samarium(II) iodide - cyclization

References

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1

Present address: Meiji Pharmaceutical University, 2-522-1 Noshio, Kiyose, Tokyo 204-8588, Japan.

8

Compounds 2 and 4 were prepared as shown in Scheme [4] .

9

Typical procedure: To a solution of SmI₂ (0.29 mmol) in THF (0.9 mL)-HMPA (0.15 mL) was added 2 (0.12 mmol) in THF (0.3 mL) at r.t. under an argon atmosphere. The reaction mixture was stirred for 5 min at this temperature, quenched with aqueous NH₄Cl and extracted with Et₂O. The ethereal solution was dried over MgSO₄. Following removal of solvent under reduced pressure, the crude product was purified by silica gel column chromatography to give 3 in 70% yield.

10

trans-Configuration of 3 was determined by chemical conversion from 3 to dihydrogeijeren [15] as illustrated in Scheme [5] .

11

Compound 6 was prepared as indicated in Scheme [6] .

12

Cyclized product 7 in pure form was obtained only in 2% yield, the other portion being present in a complex mixture.