Aqueous metal-mediated reactions and their applications in natural product syntheses
Description
The research includes two parts: methodology studies of metal-mediated reactions, and applications of the methodology in natural product syntheses Part one. Methodology studies. Section 1: Aqueous indium-mediated allylation of various aldhehydes with 3-bromo-2-chloro-1-propene followed by ozonolysis produced $\beta$-hydroxyl esters Section 2: In an effort to develop concise syntheses of ketoses, the aqueous indium-mediated reactions between a number of aldehydes and 4-bromo-2-butyn-1-ol were investigated. Benzaldehyde was treated with a variety of propargyl bromides bearing different substituents. In the presence of a chelating group on the propargyl bromide, the reaction consistently gave a mixture of allene and homopropargyl alcohol Section 3: Barbier-Grignard type reactions between carbonyl compounds and allyl halides mediated by indium, tin, and zinc under neat condition were investigated. The reactions between various carbonyl compounds and allyl bromide mediated by indium proceeded smoothly to give the corresponding allylation products at room temperature under atomsphere, with no homo-coupling products detected. Zinc and tin were also found to mediate the reaction, although less effectively than indium Section 4: Manganese-mediated allylation in aqueous medium was investigated. Manganese combined with a catalytic amount of copper effectively mediated the allylation between aryl aldehydes and allyl chloride in water, whereas either manganese or copper alone showed no mediating reactivity. In both cases of inter- and intramolecular competition studies, allyl chloride reacted exclusively with aromatic aldehydes, in the presence of aliphatic aldehydes Part two. Natural product syntheses. Section 1: The model study of a two-direction synthesis toward all syn polyene fragments through palladium-catalyzed rearrangement and toward all syn 1,3-polyol fragments through indium-mediated stereoselective allylation was investigated. Several unsuccessful synthetic attempts toward polyene fragments were made starting from 1,7-octadiyne. In the case of polyol, an attempt to prepare substrates for the model study was made Section 2: (+) Goniofufurone was synthesized from D-glucurono-6,3-lactone through an aqueous indium-mediated regio- and stereoselective allenylation of carbonyl compounds in a critical step. As a model study, the aqueous indium-mediated coupling reactions between 3-bromo-1-propynylbenzene and several carbohydrate substrates were investigated. The application of this indium method to the synthesis of (+)-Goniobutenolide A and ($-$)-Goniobutenolide B is still under investigation