Exposure of cycloalkenylalkylphosphonates 1 to oxidative cleavage conditions, followed by treatment with 1.5 equivalents of DBU in DCM (or NaH in THF) gives rise to homologated cycloalkenones 2 in good to excellent yields. Subjecting cycloalk-2-enylphosphonates 3 to identical conditions provides the one-carbon ring-contracted compounds 4 in excellent yields. Exposure of γ,δ-unsaturated ketophosphonates 6 to oxidative cleavage conditions followed by treatment with base affords cyclopentenone products 7 in good overall yields. Since diversely substituted allylic phosphonates can be efficiently prepared from cycloalkenes, cycloalkanones, and cycloalkenones in high yields by known protocols, this method may offer a practical alternative to existing methods for effecting one-carbon ring expansion, ring contraction, and annulation reactions. The application of these methods towards the total synthesis of two naturally occurring sesquiterpenes, jambolanin C and sootepdienone, will be presented.

Ring expansion, ring contraction, and annulation reactions of allylic phosphonates under oxidative cleavage/basic conditions: Application to the total synthesis of naturally occuring sequiterpenes

256th National Meeting (2018)

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