I. Michael additions to 1-bromo-1-nitroalkenes ; II. N-heterocyclic carbene-catalyzed oxidative esterification of aldehydes
Date of Issue2015
School of Physical and Mathematical Sciences
Chapter 1 Michael Additions to 1-Bromo-1-nitroalkene The beta-bromo-beta-nitrostyrenes, due to the existence of bromo and nitro functionalities, were often shown to be versatile Michael acceptors. This thesis work focused on the development of new methodologies of Michael addtions to beta-bromo-beta-nitrostyrenes. In the first part, the reaction of 1,3-diphenylthiourea and beta-bromo-beta-nitrostyrenes afforded 2-iminothiazole in moderate to good yields. The domino reaction provided a new, mild and environmental benign process for the fast and efficient synthesis of highly-functionalized 2-iminothiazoles.In the second part, the Ag(I) catalyzed addition of alpha-ethereal carbon radicals to beta-bromo-beta-nitrostyrenes under mild conditions constituted the C-C bond formation at the otherwise unreactive alpha-C-H position of cyclic ethers. The reaction was conducted in the air to generate the dioxygen incorporated product. It provided a useful synthetic tool for the preparation of various ether derivatives.Chapter 2 N-heterocyclic Carbene-Catalyzed Oxidative Esterification of Aldehydes N-heterocyclic Carbenes (NHC)-catalyzed one pot of esterification of aldehydes via inernal redox esterification has become prominent. In this work, a mild NHC-catalyzed transformation of cinnamyl cinnamate from cinnamaldehyde by employing air oxygen as an oxidant has been developed. This is an alternative method for the synthesis of esters from reactive alkyl halides and alpha,beta-unsaturated or aromatic aldehydes. Aldehydes with electron-withdrawing groups comparatively gave better yields than that with electron-donating groups. A significant feature of this protocol is that the reaction proceeds without cis-trans isomerization of the alpha-beta-olefinic linkage in the cinnamyl cinnamate derivatives. When MnO2 was used as oxidant instead of air oxygen, aromatic aldehydes generally provide ester in good yields.