Tsuneo KAWANOBE, Minoru IWAMOTO,
and Massanao MATSUI
(±)-cis-g-Irone and his trans-isomer were synthesized via 2,3-sigmatropic rearrangement of 1-hydroxymethyl-3,3,4-trimethyl-1-cyclohexene.
Reagents : a) Raney Ni, H2,
n-hexane; b) CrO3, H2SO4, acetone; c)
NaH, toluene then MeLi, MeONa and HCO2Et; d) Ethyl vinyl
ether, H3PO4; e) NaBH4, EtOH; f) Mesyl
chloride, Et3N; ii. N,N-dimethylaminoacetonitrile,
K2CO3; iii. AgNO3, H2O; g)
|The key step, 2-3 sigmatropic rearrangement, afforded a cis
/ trans mixture of aldehydes in 3/7 ration.
After a distillation by using aspinnig band type of apparatus to give cis-aldehyde, a Wittig reaction gave pure cis-g-irone in 2.5% overall yield.