Studies On The Total Synthesis Of Naturally Occurring Stilbene Dimers And Reaction Mechanism Of Some Halonium Salts Under Basic Conditions

This thesis mainly focused on the total synthesis of a few naturally occurring stilbene dimers and study of the reaction mechanism of some halonium salts under basic conditions, including the following six parts:Chapter 1. The progress on the study of naturally occurring stilbene oligomers and their biosynthesis(review)The review introduced the progress on the study of the structures and classification, biological activities, spectrum characteristic and biosynthesis of naturally occurring stilbene oligomers.Chapter 2. Total synthesis of (±)-Shegansu B, Gnetuhainin F, (±)-Maackin A and (±)-Cassigarol EIsorhapontigenin (13) and piceatannol (14) were prepared from 3, 5-dihydroxybenzoic acid in seven steps. Oxidative coupling of 13 and 14 with HRP/H2O2 gave their respective dimeric compounds. The first total synthesis of Gnetuhainin F, (±)-Maackin A and (±)-Cassigarol E was described and the oxidative coupling yield of synthesis of (±)-Shegansu B was higher than that in literatures.Chapter 3. First total synthesis of (±)-Quadrangularin A3,5-di-t-butyl-resveratrol (15) as a coupling precursor was prepared from 3,5-dihydroxybenzoic acid in seven steps. The regioselcetive coupling product 16 was obtained by oxidative coupling reaction of 15 with HRP/H₂O₂. The first total synthesis of (±)-Quadrangularin A was finished followed by the prototropicrearragement of 16 and the removal of t-butyl protecting groups. Chapter 4. Study on the total synthesis of (±)-Gnetulin and its analoguesRegioselective oxidative coupling approach to the synthesis of (±)-Gnetulin and its analogues were studied. The key coupling reaction of 5-f-butyl-isorhapontigenin (13) with HRP/H2O2 gave two stilbene trimers (15 and 16). which might be converted into target moleculars by proper organic transformation and this work is ongoing.Chapter 5. Study on the total synthesis of (±)-Gnetuhainin QAn efficient method for the total synthesis of (±)-Gnetuhainin Q was studied. The cross-coupling reaction of resveratrol (5) and 5-f-butyl-isorhapontigenin (7) by using Ag2CC>3 as oxidant gave the key coupling dimer 8. The subsequent work of the removal of the f-butyl protecting group from 8 to provide (±)-Gnetuhainin Q is ongoing.Chapter 6. Study on the reaction mechanism of some halonium salts under basic conditionsReactions of 3,7-dinitrodibenzobromolium salt (la) with primary and secondary amines were studied. The result that the major products 6a⁶e and the minor product 7a⁷e are regioisomers supports a mechanism with the substituted benzyne 4a as the intermediate. It provides powerful backing for this mechanism that the formed benzyne intermediates of some halonium salts (la^lc and 9-12) under basic conditions were successfully trapped using anthracene. The structures of the corresponding trapped products were established by {H NMR, MS and IR spectroscopy. The crystal and molecular structure of 8a was determined by X-ray analysis. The dihedral angle between two phenyl rings of the biphenyl part of 8a is77° , showing that 8a is an axial-chiral molecule.This thesis concerned six sections above, in which the total synthesis of five naturally stilbene dimers were finished. A novel efficient approach to several types of stilbene oligomers were developed and studies on the synthesis of several stilbene dimers by this approach were discussed. Moreover, the reaction mechanism of the formed benayne intermediate of some halonium salts under basic conditions was verified. Over 60 compounds were synthesized in this thesis with over 30 were new ones. The structures of one new compound was determined by X-ray crystal structural analysis. The structures of the new compounds were identified by spectral analysis methods .