ABSTRACT
The intramolecular cyclocarbonylation reaction with palladium-complexed dendrimers on silica is a very effective method for the regioselective synthesis of methylene 8-, 9-, and 10-membered rings. The heterogeneous dendritic catalysts are easily recovered by simple filtration and reused for up to 10 cycles with only a slight loss of activity. Asymmetric hydrogenation of the resulting unsaturated heterocycles affords optically active tricyclic lactams in excellent yields and in high enantiomeric excess. This process can tolerate a wide array of functional groups, including halide, ether, nitrile, ketone, and ester. Moreover, the variation of heteroatom on the rings does not have any influence on the efficiency and enantioselectivity of the reaction.
Subject(s)
Lactams, Macrocyclic/chemical synthesis , Crystallography, X-Ray , Cyclization , Hydrogenation , Lactams, Macrocyclic/chemistry , Organometallic Compounds/chemistry , Rhodium/chemistry , StereoisomerismABSTRACT
Intramolecular cyclocarbonylation reactions with palladium-complexed dendrimers on silica gel as catalysts are very effective for the synthesis of twelve- to eighteen-membered ring macrocycles. This process can tolerate a wide variety of functional groups, including halide, ether, ketone, and ester. The heterogeneous dendritic catalysts facilitate excellent substrate reactivity, affording oxygen-, nitrogen-, or sulfur-containing tricyclic heterocycles in 70-92 % yields. Importantly, these systems are easily recovered by simple filtration and reused several times with only a slight loss of activity.
Subject(s)
Dendrimers/chemistry , Macrocyclic Compounds/chemical synthesis , Organometallic Compounds/chemistry , Palladium/chemistry , Silicon Dioxide/chemistry , Catalysis , Cyclization , Macrocyclic Compounds/chemistry , Molecular Structure , Silica GelABSTRACT
Palladium-complexed dendrimers supported on silica were evaluated as catalysts for intramolecular carbonylation reactions. The results showed that dendritic catalysts display high activity, affording oxygen, nitrogen, or sulfur-containing seven- or eight-membered ring fused heterocycles in excellent yields. Moreover, these catalysts have competitive advantages in that they can be easily recovered by simple filtration in air and reused for up to eight cycles with only a slight loss of activity.
Subject(s)
Aniline Compounds/chemical synthesis , Organometallic Compounds/chemistry , Palladium/chemistry , Silicon Dioxide/chemistry , Aniline Compounds/chemistry , Catalysis , Cyclization , Molecular Structure , Nitrogen/chemistry , Oxygen/chemistry , Sulfur/chemistryABSTRACT
Rhodium-complexed dendrimers, supported on a resin, were evaluated as catalysts for the carbonylative ring expansion reactions of a variety of aziridines with carbon monoxide to give beta-lactams. The effects of reaction temperature, solvent, time, and pressure of carbon monoxide on this transformation were also investigated. The dendritic catalysts showed comparable activity to the homogeneous analogue. More importantly, this catalytic system can be easily recovered by simple filtration and recycled without significant loss of activity.
ABSTRACT
Rhodium-complexed dendrimers supported on a resin were evaluated as catalysts for the hydroformylation of aryl olefins and vinyl esters. The results showed the reactions proceeded very efficiently at room temperature with excellent yields. Outstanding selectivity for the branched aldehydes was also observed in all cases. The dendritic catalysts can be recycled by simple filtration and reused even up to the tenth cycle without loss of activity and selectivity. These results represent a dramatic improvement over those previously described for rhodium-catalyzed (dendrimer and nondendrimer based) hydroformylation reactions.
