Silicon-Controlled Intramolecular Thermal H-ENE Reaction.
A New Access to a Key Intermediate of (±)-Cis-g-Irone.

Honoré Monti,* Gilles Laval, and Michel Féraud

    As part of our interest in the ene reaction of allylsilanes [26], [27], we report a significant improvement in the diastereoselective synthesis of new access to a the key intermediate 3 starting from Hagemann's ester 5 in the synthesis of (±)-cis-g-irone with high chemocontrol thermal H-ene reaction and significant improved overall yield.

Reagents : a) i. 2 MeLi, CuI, Et2O, -5°C ii. HMPT, ClPO(OEt)2, THF; b) ClMgCH2SiMe3, NiCl2(dppp) cat., THF, reflux; c) LiAlH4, Et2O, -20°C then rt.;  d) methyl propiolate, N-methylmorpholine, Et2O, rt.; e) Decaline, sealed tube, 250°C; f) p-toluene sulfinic acid , CH2Cl2, rt.
    In summary, the intramolecular thermal H-ene reaction of an allysilane has been studied in terms of chemo- and regioselectivity. This has been developed into a strategy for a new access to a key intermediate in the diastereoselective synthesis of(±)-cis-g-irone with total chemocontrol and 56% overall yield.
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