Synthesis of the 1,2-seco fusicoccane diterpene skeleton by Stille coupling reaction between the highly functionalized A and C ring segments of cotylenin A

1-Hydroxy-14-isopropyl-3β-methoxymethyl-7β,11β-dimethyl-3α-[((2-trimethylsilyl)ethoxy)methoxy]-1,2-secofusicocca-8,10(14)-dien-2-one, a highly functionalized 1,2-seco fusicoccane diterpene skeleton related to cotylenin A was synthesized in a convergent manner. The A ring segment, i. e., (1′R,2S, 2′E,5S)-2-methoxymethyl-5-[1′-methyl-3'-(trimethylstannyl)prop-2-enyl]-2-[((2″-trimethylsilyl)ethoxy)methoxy]cyclopentanone, was synthesized in 20.1% yield over 18 steps from known (S)-5-isopropenyl-2-methylcyclopent-1-enecarbaldehyde. This was coupled with the C ring segment, i. e., (R)-5-hydroxymethyl-2-isopropyl-5-methylcyclopent-1-en-1-yl trifluoromethylsulfonate, which was prepared according to our previous report. The Stille coupling reaction between alkenylstannane and sterically hindered triflate proceeded successfully in the presence of PEPPSI-SIPr (85%), and the total yield of the target molecule was 17.1% over the longest linear sequences (19 steps) from (S)-5-isopropenyl-2-methylcyclopent-1-enecarbaldehyde.

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