Exploration Work Toward The Total Synthesis Of Heliannuol F

In recent years, pesticides have been experiencing a rapid development, and particularlysynthetic pesticides based on natural products which are degradable with high bioactivitieshave emerged and been in vast progress. Sunflowers exhibit strong cytotoxicity tosurrounding plants, for which reason they have attracted a great deal of interest of researchers.As a result, natural sesquiterpenoids Heliannuols have been isolated and synthesizedgradually.This work focuses on the Heliannuol F, which possesses strong cytotoxicity to bothmonocotyledon and dicotyledon but is hardly synthesized so far. We analyzed its originalstructure, attempted to synthesized it with several different methods and drew someconclusions as follows.1. Because of the bare carbonyl group of heliannuol F, we protected it withdipropylsulfide and achieved polarity reversal in situ. However, out of our expectation, wefound that the structure was highly unstable after deprotection of the hydroxyl for theconcurrent effects of the double bond and the carbonyl group. As the property of protectinggroup affected the deprotection process after cyclization, the carbonyl group could only beconstructed by functional group transformation.2. Based on functional group transformation to achieve the carbonyl group, we decidedto choose the double bond as the precursor and establish the seven-membered ring by RCMcyclization.The fact was that once the hydroxyl group of coumarin was deprotected,decarboxylation did not lead to the desired compound on account of the big conjugatedsystem turning to be electron-rich.3. With double bond still being selected precursor of the carbonyl group, we employedthe methodology of Pd-catalyzed cyclization to build the seven-membered ring, which was tobe found that it was barely impossible to synthesized the precursor reactant.