Studies On Selective Control Of Transition Metal-Catalyzed Reactions

This thesis focuses on the selective control of iron, palladium and other transition metal-catalyzed reactions. We have developed a novel and useful synthetic methodology to prepare some important compounds by selective control reactions. In the present work, the first ring expansion of alkynylcyclopropyl alkanols catalyzed by FeCl2 highly selectively leading to alkynylcyclobutanols under mild conditions was achieved. The cyclobutanols are a common structural unit of natural products and are of great importance in the area of pharmaceuticals and are versatile building blocks for further transformation as well. Moreover, we demonstrate an efficient and highly selective Heck reaction of organic halides with allylic esters by avoidingβ-acetate orβ-carbonate elimination. The resulting substituted allylic esters are amenable to further functional group transformations.This thesis includes the following two sections:1. Studies on the Selective Control of Alkynyl Cyclopropyl Alkanols with Iron-CatalystsWe have developed FeCl2 catalyzed ring expansion of alkynylcyclopropyl alkanols leading to alkynylcyclobutanols, which are a common structural unit of natural products and are of great importance in the area of pharmaceuticals and are versatile building blocks for further transformation as well. The regioselectivity of this transformation was high. With the optimized reaction conditions, the scope of the FeCl2 catalyzed ring expansion was subsequently investigated. A range of secondary alkanols were tolerated for this ring expansion. The structure of alkynylcyclobutanols which is contradictory with the regioselectivity reported by Larock, was determined by 1H-1H NOESY, DEPT, 1H-1H COSY, and 1H-13C HMQC spectra. We also found that when alkyl group is replaced by phenyl group, the reaction produced noncyclic product (E)-3-benzylidene-5-phenylpent-4-yn-1-ol highly selectively. We also synthesized chiral substrate to study the mechanism of the reactions. We think that the employed Fe-catalyst is suggested to facilitate the reaction by a dual function as both a Lewis acid and coordination reagent with alkynes. These reactions are easy to operate under mild conditions. The discovered ring expansion here may provide an efficient method to construct substitute alkynylcyclobutanols.2. Ligand Free Pd-Catalyzed Highly Selective Arylation of Allylic Esters with Retention of the Traditional Leaving GroupWe have developed a Pd-catalyzed highly selective Heck reaction between organic halides and allylic esters. Theβ-elimination of the OAc or OCO2Me group is avoided in this reaction, which could serve as a useful supplement to the traditional Heck reaction and the Tsuji-Trost allylation. The reaction conditions are mild, the reaction can be carried out in a straight forward manner in air and no ligand is required. This method could provide a useful tool for the synthesis of substituted allylicalcohols. The mechanism of the reaction is preliminarily studied .