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We report a Michael-type cyanation reaction of coumarins by using CO2 as a catalyst. The delivery of the nucleophilic cyanide was realized by catalytic amounts of CO2, which forms cyanoformate and bicarbonate in the presence of water. Under ambient conditions, CO2-catalyzed reactions afforded high chemo- and diastereoselectivity of β-nitrile carbonyls, whereas only low reactivities were observed under argon or N2. Computational and experimental data suggest the catalytic role of CO2, which functions as a Lewis acid, and a protecting group to mask the reactivity of the product, suppressing byproducts and polymerization. The utility of this convenient method was demonstrated by preparing biologically relevant heterocyclic compounds with ease.

A chiral cobalt(III) complex (1e) was synthesized by the interaction of cobalt(II) acetate and ferrocenium hexafluorophosphate with a chiral dinuclear macrocyclic salen ligand that was derived from 1R,2R-(-)-1,2-diaminocyclohexane with trigol bis-aldehyde. A variety of epoxides and glycidyl ethers were suitable substrates for the reaction with water in the presence of chiral macrocyclic salen complex 1e at room temperature to afford chiral epoxides and diols by hydrolytic kinetic resolution (HKR). Excellent yields (47% with respect to the epoxides, 53% with respect to the diols) and high enantioselectivity (ee>99% for the epoxides, up to 96% for the diols) were achieved in 2.5-16 h. The Co(III) macrocyclic salen complex (1e) maintained its performance on a multigram scale and was expediently recycled a number of times. We further extended our study of chiral epoxides that were synthesized by using HKR to the synthesis of chiral drug molecules (R)-mexiletine and (S)-propranolol.

A series of chiral polymeric Co(III) salen complexes based on a number of achiral and chiral linkers were synthesized and their catalytic performances were assessed in asymmetric hydrolytic kinetic resolution of terminal epoxides. The effect of the linker were judiciously studied and it was found that in case of chiral BINOL based polymeric salen complex 1, there was certain enrichment in catalyst reactivity and enantioselectivity of the unreacted epoxide particularly in the case of shor t as well as long chain aliphatic epoxides. Good isolated yield of the unreacted epoxide (up to 46% out of 50% theoretical yield) along with high enantioselectivity (up to >99%) were obtained in most of the cases using catalyst 1. Further studies exhibited that the catalyst 1 could retain its catalytic activity for six cycles under the present reaction conditions without any significant loss in activity and enantioselectivity. To show the practical applicability of the above synthesized catalyst we have car ried out synthesis of some potent chiral -blockers using complex 1 in moderate yield and high enantioselectivity. The DFT (M06 -L/6-31+G**//ONIOM(B3LYP/6-31G*:STO-3G)) calculations revealed that the chiral BIN OL linker influences the enantioselectivity with Co(III)salen complexes. Further, the transition state calculations show that the R-BINOL linker with (S,S)-(salen)Co(III) complex is energetically preferred over the corresponding S-BINOL linker with (S,S)-(salen)Co(III) complex for HKR of 1,2-epoxyhexane. The role of non-covalent C-H… π interaction and steric effects has been discussed to control the HKR reaction of 1,2 -epoxyhexane.

A protocol for the carbonylative synthesis of acyl amidines from aryl halides, amidines, and carbon monoxide catalyzed by Pd(0) is reported herein. Notably, carbon monoxide is generated ex situ from a solid CO source, and several productive palladium ligands were identified with complementary benefits and substrate scope. Furthermore, sequential one-pot, two-step protocols for the synthesis of 1,2,4-triazoles and 1,2,4-oxadiazoles via acyl amidine intermediates are reported. In addition, this approach was extended to isotopic labeling using [ 11 C]carbon monoxide to allow, for the first time, synthesis of 11 C-labeled acyl amidines as well as a 11 C-labeled 1,2,4-oxadiazole.

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