Synthesis of C-seco Limonoid Model Insect Antifeedants Related to
Ohchinolide and Nimbolidin

Abstract

A concise and stereoselective synthesis of a CDE-seco limonoid related to ohchinolide and nimbolidin was accomplished in eleven and twelve steps, respectively, from α-cyclocitral. Opening of the C ring was first attempted by a retro-Claisen reaction, whereby a very unusual rearrangement occurred. However, the ring-opening was successfully accomplished by a selective Baeyer-Villiger reaction.

Key words

stereoselective synthesis - allylic rearrangement - C-seco limonoids - ohchinolide - nimbolidin

References

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7

Crystallographic data (excluding structure factors) for the structures 6 and 9a have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication nos. CCDC 159675 and CCDC 159676, respectively. Copies of the data can be obtained free of charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK. Fax: [phone] or e-mail: [e-mail].

9

Proposals have been made regarding the hypothetical biogenesis of C-seco limonoids such as ohchinolide, arising from the hydrolytic cleavage of the 12β-hydroxy-14,15β-oxide, which can be opened to give the 12-aldehyde-Δ^13,14-15β-ol intermediate, followed by attack of the hydrate aldehyde to the allylic carbon C-15 with inversion and later oxidation to lactone (Scheme [10] ).

10

All compounds synthesised are racemic although, only one enantiomer is depicted.

13

Essays of insect antifeedant activity of all compounds described in this work will be published in due course.