'One Pot' Wittig Olefinations In Aqueous Media & Synthesis Of Chiral P, O-Ligands And Their Application In Asymmetric Allylic Alkylation

The thesis consists of three parts: the study on "one-pot" Wittig olefmation in aqueous media;the study on synthesis of novel P,O-ligands and application in Pd-catalyzed asymmetric allylic alkylation;and the experimental section.In the first part, the details of aqueous "one-pot" Wittig olefmation are presented. A brief overview on the Wittig olefination is given, including the reaction mechanism, stereochemistry and the recent development in microwave-assisted Wittig olefination and aqueous reactions of stabilized and semistabilized ylides with aromatic aldehydes. The discussion is then focused on our results of "one-pot" Wittig reaction carried out in water. Simply by heating a suspension of an aldehyde, a halide (ethyl a-bromoacetate, a-bromoacetonitrile or a-bromoacetamide), and PPh₃ in water containing LiOH and 1.2 M LiCl, the olefin products were obtained in 70-99% yields. Most of the aqueous Wittig reactions completed within 5-30 min, except for some unreactive aldehydes, which required a longer reaction times of 1-3 h. The ratios of E:Z isomers vary with the structures of the aldehydes, ranging from 100:0 to 55:45.In the second part, our effort devoted to the synthesis of axially chiral P,O-ligands for Pd-catalyzed asymmetric allylic alkylation is addressed. An introduction is outlined on the mechanism and classification of asymmetric allylic alkylation, as well as the recent advancement in synthesis of chiral ligands. The directed ortho-metalation (DoM) via aromatic amides is briefed for use in the synthesis of our chiral P, O-ligands. Several chiral P,O-ligands were synthesized in this study with their absolute stereochemistry determined by X-ray crystal structural analysis. The newly synthesized chiral ligands were evaluated for efficiency in Pd-catalyzed asymmetric allylic alkylation.In the experimental section, the detailed reaction procedures, compound characterization data, and references are presented. The X-ray crystal structural analysis data of the chiral ligand and the HPLC charts for determination of ee of the asymmetric allylic alkylation products are given in the Appendix.