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Chiral dimeric Mn(III) salen complex with 1 R , 2 R -(−)-diaminocyclohexane collar was immobilized on short channel large pore sized silica through a long linker of {(CH 2 ) 3 –NH–melamine–piperazine} to investigate its performance in enantioselective epoxidation of chromenes, indene, styrene and cis β-methyl styrene in the presence of pyridine N -oxide (Py N O) as an axial base using aqueous NaOCl as an oxidant at 0 °C. The immobilized catalyst system showed high turnover frequency (TOF) and enantioselectivity for the smaller and bulkier alkenes like styrene, indene, 2,2-dimethylchromene and 6-cyano-2,2-dimethylchromene (ee up to 98%). These results are the best reported for heterogeneous catalyst under biphasic reaction conditions and were comparable to the dimeric Mn(III) salen system under homogeneous condition. The performance of the immobilized catalyst was retained for six reuse experiments. This protocol was extended to the synthesis of an antihypertensive drug ( S )-Levchromakalim (ee 98%) at 1 g level.

A series of new chiral monomeric and dimeric macrocyclic Mn(III) salen complexes 1 – 4 with trigol linker were synthesized, characterized (by microanalysis, IR spectroscopy, UV–vis. spectroscopy, optical rotation, and mass spectrometry), and used as catalysts in the enantioselective epoxidation of styrene, cis β-methyl styrene, indene, and chromenes in the presence of several N -oxides as an axial base and NaOCl as an oxidant at 0 °C. With the use of chiral dimeric macrocyclic catalyst 3 (2.5 mol%), enantio-pure epoxides were achieved in excellent yields (>99%) and enantioselectivities (ee up to 98% in selected cases). The recycling was demonstrated with complex 4 (recyclable up to six cycles studied with retention of enantioselectivity) in the asymmetric epoxidation of styrene. The kinetic investigation with complex 4 for the epoxidation of styrene as the representative substrate showed the first-order dependence on the catalyst and the oxidant but independent on the initial concentration of the substrate.

Chiral macrocyclic V(V) salen complexes 1a – f derived from macrocyclic ligands obtained by the reaction of 1 R ,2 R -(−) diaminocyclohexane/(1 R ,2 R )-(+)-1,2-diphenylethylenediamine with bis-aldehydes 2 and 3 were synthesized and used as efficient catalysts in asymmetric cyanation reactions. The V(V) catalysts demonstrated excellent performance (product yields and ees up to 99%) with potassium cyanide (KCN) and sodium cyanide (NaCN). The catalytic system also performed very well with a safer source of cyanide-ethyl cyanoformate to give cyanohydrin carbonates in excellent yield and ee (up to 97%). The V(V) macrocyclic salen complex 1b retained its performance at multi-gram level and was conveniently recycled for a number of times.

Various ionic liquids ( IL 1 – 9 ) based on N -methyl N′ -alkyl imidazolium salts were explored as catalytic media in cyanoethoxycarbonylation of various aldehydes. The study revealed that the alkyl chain length and counter ion of the ionic liquid are critical for the product yield. The highest product yield of cyanohydrin carbonate (up to 96%) was obtained with C 5 alkyl chain with Br − as counter ion ( IL 3 ). On the other hand PF 6 − as counter ion failed to catalyze the cyanoethoxycarbonylation reaction.

Chiral dimeric vanadium (V) salen complex (10 mol%) derived from 5,5-Methylene di-[( S,S )-{ N -(3- tert -butyl salicylidine)- N′ -(3′,5′-di- tert -butyl salicylidene)]-1,2-cyclohexanediamine] with vanadyl suphate followed by auto oxidation was used as efficient catalyst for enantioselective Strecker reaction of N -benzylimines with TMSCN at −30 °C. Excellent yield (92%) of α-aminonitrile and high chiral induction was achieved (ee up to 94%) in case of 2-methoxy substituted N -benzylimines in 10 h. The catalytic system worked well up to four cycles with retention of enantioselectivity.