Studies On N-heterocyclic Carbene(NHC) Catalyzed Asymmetric Annulation And Acylation Reactions

Catalytic reactions promoted by N-heterocyclic carbenes (NHCs) have exploded in popularity since 2004 when several new fundamental reactions were reported. These reactions are usually carried out under simple, mild reaction conditions and with exceptional selectivities. In this thesis, recent progress on NHC-catalyzed annulation and acylation reactions is initially summarized. On this basis, several NHC-catalyzed annulation and acylation reactions of aldehydes are presented. The details are summarized as following:1. By using an N-heterocyclic carbene catalyst bearing a hydroxyl moiety, the asymmetric formal [3+2] cyclization of aryl 3-bromoenals and isatins was achieved to produce a series of chiral spirooxindole-butenolides in excellent yield and high enatioselectivity. It is proposed that this raction might proceed by anNHC/hydrogen-bonding dual-activation mode. Besides, treatment of spirooxindole-butenolides with a NaBH4/NiCl2 system afforded chiral spirocyclic lactones, while the reaction of alkenyl-substituted product with aryne precursor directly furnished aromatic products via a dehydro-aromatization of the intermediacy of Diels-Alder adducts.2. By using an N-heterocyclic carbene catalyst bearing a free hydroxyl group, the asymmetric formal [3+2] cyclization of aromatic 3-bromoenals and benzofuran-2,3-dione was accomplished to form a series of chiral spirooxbenzofuran-butenolides in good yield and high enatioselectivity. This reaction tolorated a wide variety of substrates with complete regioselectivity.In deed such a [3+2] cyclization only took place at the 3-position of benzofuran-2,3-dione, without any by-product of C2-cyclization observed. This study extends the scope of reaction partner with 3-bromoenals by NHC catalysis.3. We have developed a method for the acylation of sulfamides directly using aldehydes under oxidation condition by NHC catalysis. This process extended the synthetic application of NHC catalyzed acylation reaction via acyl azolium intermediates. The reaction was carried out in mild condition with a wide range ofsubstrates, resulted in excellent yield and without any metal catalysts and ligands. This reaction expands the synthetic application of NHC-catalyzed acylation reactions, thereby affording an alternative synthetic route to N-Sulfonylcarboxamide.