The Synthesis of (±)-g-Irones

Takeshi KITAHARA, Kaichi TANIDA and Kenji MORI

(±)-g-Irones (1/9 mixture of cis- and trans-isomers and pure trans-g-irone) were synthesized via the intramolecular Diels-Alder reaction starting from 2,4-hexadienyl aniline derivative and b,b-dimethylacryloyl chloride.

Reagents : a) i. o-aminophenol, NaHCO3, EtOH;  ii. NaBH4, H2O; b) b,b-dimethylacryloyl chloride, Bz, K2CO3, Py; c) EtMgBr, 140°C, xylene; d) MeOH, MeONa; e) H2, Pd/C, THF-AcOEt; f) HNO3, AcOH; g) i. KOH, THF;
ii. P-TsOH, toluene; h) i. Dibal-H, DME, toluene; ii. Ph3P=CHCOCH3, Toluene; i) i. KI, H3PO4, CH2Cl2; ii. NaHCO3; j) NO2C6H4SeCN, NaBH4, EtOH; ii. H2O2, THF.

This is the first synthesis of cis-g-irone, but it's a mixture (1/9).
Unfortunately, the final product consisted mainly of the trans-isomer because of 
epimerization during the  transformation from A.