Ergosterol And Its Application In Natural Product Synthesis

The thesis describes our efforts for the study of the reactions of B/C/D ring ofergosterol and the synthesis of some natural products whose structures are similar tothe active ingredient of Cordyceps.Based on the products of homoallylic alcohol rearrangement reaction of A/Bring and singlet oxygen cycloaddition reaction of B ring of ergoserol, we explored theapplication in the synthesis of chemical composition of Cordyceps. In the process ofrearrangement reaction of A/B ring of ergoserol, besides desired C6-OH product, weunexpectedly gained main elimination product when feeding mode, reaction timeand work-up were changed. The result was the supplement of method of obtainingelimination product when ergosterol was treated with acid. An oxidation of theproduct of homoallylic alcohol rearrangement reaction, followed by an allylicoxidation and an elimination provided compound2-2, whose C6-carbonyl wasreduced, followed by singlet oxygen cycloaddition reaction provided compound2-3.A key intermediate2-3was prepared starting from ergosterol in7steps in11%overall yield. The further transformations to natural product1-47and1-49were alsostudiedNatural product1-42was prepared in the singlet oxygen cycloaddition reactionof B ring of ergoserol. We found a reaction condition to reduce the highly stable α-cycloaddition product of ergosterol and singlet oxygen with zinc and nickel-aluminuminstead of zinc/acetic acid.In the transformation of peroxide reduction product2-27，the reaction products2-34和2-36of C8-OH were obtained by chromium trioxide oxidation and SN2’reaction.Tandem elimination ring-opening/epoxidation/rearrangement product2-44wasunexpectedly obtained in exploring the ring-opening/ring expansion of compound 2-40, the singlet oxygen cycloaddition product of B ring of ergosterol. The possiblerecation mechanism was showed.