Cycloaraneosene

Double stereodifferentialing Hiyarna reactions are the key steps in the total synthesis of ( + )- and (-)-nephromopsinic acid12 and (-)- and ( + )-dihydrocanadensolide33. The enantiomcrically pure diterpene cycloaraneosene is assembled by two chromium(II) chloride mediated coupling reactions from (3S,87 )-9-benzyloxy-7-chloroirid-1-ene (3) and (3[Pg.444]

Section 1.13.5 Miscellaneous reactions. Takeshita and coworkers reported the remarkable use of intramolecular ene reactions to form cycloheptanes and cyclooctanes. Pyrolysis of (216) in toluene at 200 C gives 97% of the cycloheptane (215). Reaction of (216) with SnCU in THF gives 85% of cyclooctane (217), which is an intermediate in the synthesis of cycloaraneosene. 

The unsaturated aldehyde 424 on heating to 200 °C in toluene provided a 97% yield of the hydroazulene derivative 425, in a probably stereocontroUed process, whereas SnCl4 in an electronically directed cyclization gave rise to the cycloaraneosene precursor 426 in 85% yield. 

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