Studies on Poly(N-Heterocyclic Carbene) and Base Catalysis for Organic Reactions

Abstract

Part I. Poly (N-heterocyclic carbene) catalyzed reactions

Chapter 1. Poly (4-vinylimidazolium) iodides: a highly recyclable organocatalyst precursor for benzoin condensation reaction The development of highly efficient, recyclable poly(4-vinylimidazolium) iodides (2) for the benzoin condensation reaction under mild reaction conditions is discussed: poly(4-vinyl N-heterocyclic carbene)s (3) obtained from 2 showed higher catalytic activity than monomeric 4-vinyl N-heterocyclic carbene and could be successfully recovered and reused over seven times without loss of performance.

Chapter 2. Poly (4-vinylimidazolium)s/ Diazabicyclo[5.4.0]undec-7-ene/ Zinc(II) Bromide-Catalyzed Cycloaddition of Carbon Dioxide to Epoxides Poly(4-vinylimidazolium)s (2) with diazabicyclo[5.4.0]undec-7-ene (DBU) and zinc bromide (ZnBr2) are used as a highly efficient catalyst for chemical fixation of carbon dioxide. This catalytic system has been applied for preparation of cyclic carbonates from terminal epoxides and carbon dioxide. Many functional groups are well tolerated in the reactions. Moreover, the catalytic system was found to catalyze the conversion of more sterically congested epoxides which are generally considered challenging substrates for fabricating the cyclic organic carbonates. In addition, the disubstituted epoxides are found to react with retention of configuration. The polymer precatalyst is easily recovered and reused.

Part II. Base-catalyzed organic reactions

Chapter 1. Potassium Phosphate-Catalyzed One-pot Synthesis of 3-Aryl-2-oxazolidinones from Epoxides, Amines, and an Atmospheric Carbon Dioxide Potassium phosphate was found to be a highly active catalyst in the three-component cycloaddition of amine, epoxide, and carbon dioxide in DMF at ambient temperature to form 3-aryl-2-oxazolidinones. Atmospheric CO2 and a broad range of amines were employed in this transformation. Aryl isocyanate and 1,2-aminoalcohol were generated in situ as key intermediates. This one-pot reaction is applicable to a variety of terminal aryl epoxides and amines. The key advantages are high yields, simple work-up, inexpensive catalyst, and a practical ten gram-scale synthesis.

Chapter 2. Base-catalyzed one-pot synthesis of unsymmetric fluorenes from aromatic ortho-dialdehydes and 1,3-dicarbonyl compounds A synthetic route for the preparation of unsymmetrically polysubstituted fluorenes was developed via the base-catalyzed one-pot domino reactions of aromatic ortho-dialdehydes with 1,3-dicarbonyl compounds. This protocol provides an expeditious access to indene-fused polycyclic aromatic hydrocarbons such as benzo[b]fluorene and 13H-indeno[1,2-b]anthracene skeletons.