Current Organocatalysis - Volume 1, Issue 2, 2014

The organo-catalyzed reaction of chalcones with acetone has been described. Pyrrolidine has been found to catalyse the cascade Michael-aldol-dehydration of chalcones and acetone to produce 3,5-diaryl cyclohexenones under mild conditions with good yields. The organocatalytic methodology tolerated a range of substituents on both the aromatic rings of chalcones. The cyclohexenones produced are known to be the precursors for 3,5-diarylphenols, 3,5-diarylanilines and complex heterocycles.

Nine metal-organic frameworks, [M(PDA), M(BTC), M(PTC)] (M=Cu, Co, Mn; H2PDA= pyridine-2,6- dicarboxylic, H3BTC= 1,3,5-benzenetricarboxylic acid , H3PTC= pyridine-2,4,6-tricarboxylate), containing respectively Cu2+, Co2+, Mn2+ ions and carboxylate ligands (H2PDA, H3BTC, H3PTC). They can be used as valuable heterogeneous catalysts since they are easily separated and reused from the reaction systems, and possess single catalytic active sites in their frameworks which are characteristic of the homogenous catalysts. In addition, N-hydroxyphthalimide (NHPI) has been also revealed to be valuable organocatalyst for free-radical processes and found ample applications in promoting the aerobic oxidation of a wide range of organic compounds. We present here a heterogeneous protocol by adsorbing NHPI in MOFs to obtain the novel NHPI/MOFs catalytic system. The allylic oxidation of α-isophorone (α-IP) into ketoisophorone (KIP) utilizing the NHPI/MOFs as heterogeneous catalysts with moleular oxygen as primary terminal oxidant under solvent- free condition was conducted. The results show that NHPI/Co(BTC) obtain optimum catalytic efficiency affording 36.6% conservation of α-IP and 81.7% KIP selectivity. The catalyst can be isolated easily from the reaction system by simple filtration and recycle without significant degradation in activity. The oxidations fulfill the requirement of green chemistry concept in terms of environmental benignity and sustainability.

One of the most important carbon-carbon bond forming reactions in organic synthesis is the cyanation of carbonyl compounds. The resulting cyanohydrins are key building blocks for many other important compounds, namely, α- hydroxy acids, α-hydroxy ketones, primary and secondary α-hydroxy amines, α-hydroxy esters and α-amino acids, which are essential in areas such as fine chemistry, agrochemicals and pharmaceuticals. Cyanohydrin synthesis can be catalyzed by enzymes, metal complexes, inorganic and organic componds. The initial synthetic methods have been extensively explored however the organocatalyzed reaction has been referred to in more limited extent. In this paper we will review the cyanation of aldehydes and ketones in the presence of organocatalysts, addressing both the formation of racemic and nonracemic cyanohydrins.

The enantioselective desymmetrization is regarded as an effective strategy for producing chiral compounds from achiral substrates. The past decade saw the establishment of organocatalysis in organic synthesis and also organocatalytic desymmetrizations have emerged in recent years. In particular, bifunctional organocatalysts have shown the ability to promote enantioselective desymmetrizations enabling simultaneous covalent and/or non-covalent activations of the reagents. Many classes of prochiral and meso compounds were efficiently desymmetrized, being cyclic anhydrides ringopening and diols acylation the most widely employed transformations. The goal of this review is to give a comprehensive overview on the developed strategies in the field of the enantioselective desymmetrizations promoted by bifunctional organocatalysts.