Further study on synthesis of the cyclobakuchiols

Two results are described. First, quinic acid was transformed into the monoacetate of 2-cyclohexene-1,4-diol. The Ni-catalyzed allylic substitution of the monoacetate with CH2C(Me)MgBr/ZnCl2/TMEDA followed by oxidation of the resulting SN2-type product afforded the 4-(CH2C(Me))-substituted 2-cyclohexenone. BF3·OEt2-assisted 1,4-addition of the enone with (4-MeOC6H4)2Cu(MgBr)·MgBr2 furnished the ketone, which is the key intermediate for the synthesis of cyclobakuchiols A and C. Second, the allylic picolinate with CMe2(OTES) and 4-MeOC6H4 groups at 3 and 4 positions of the cyclohexane ring was synthesized through 1,4-addition of (4-MeOC6H4)2Cu(MgBr)·MgBr2 to 4-(CMe2(OTES))-2-cyclohexenone. Allylic substitution of this picolinate followed by deprotection furnished cyclobakuchiol C. Furthermore, the methyl ether of cyclobakuchiol C was transformed to cyclobakuchiol A.

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