Ajay Jakhar

Unravelling a New Class of Chiral Organocatalyst for Asymmetric Ring-Opening Reaction of Meso Epoxides with Anilines

Chiral sulfinamide based organocatalyst 11 was synthesized from readily available starting materials and used for the asymmetric ring-opening (ARO) reaction of meso epoxides with anilines. A high yield (up to 95%) of chiral β-amino alcohols with excellent enantioselectivity (ee up to 99%) was achieved in 24-30 h at rt under optimized reaction conditions. A probable mechanism for the catalytic ARO reaction is envisaged by (1)H and (13)C NMR experiments.

Asymmetric Hydrocyanation of Nitroolefins Catalyzed by an Aluminum(III) Salen Complex

Chiral AlIII salen complexes were synthesized and used as catalysts for the asymmetric hydrocyanation of nitroolefins using 4‐phenylpyridine N‐oxide as an additive and trimethylsilyl cyanide (TMSCN) as a source of cyanide. An excellent yield of β‐nitronitrile (87 %) and enantioselectivity (90 %) were achieved if (2‐nitrovinyl)cyclohexane was used as a substrate at −15 °C in 16 h. To understand the interaction of the AlIII salen complex and additive, NMR and IR spectroscopic studies revealed that 4‐phenylpyridine N‐oxide acts both as an axial ligand and helps to activate the cyanide source TMSCN, which thereby increases the reactivity. A catalytic cycle was proposed based on the spectroscopic studies.

Catalytic asymmetric synthesis of enantioenriched β-nitronitrile bearing a C-CF3 stereogenic center

CF3 substituted β-nitronitriles with an all-carbon quaternary stereogenic center have been synthesized via asymmetric cyanation reaction. In situ generated chiral TiIV salen complexes were used as catalysts for asymmetric addition of TMSCN to nitroolefins containing a trifluoromethylated prochiral center in the β-position, to afford the corresponding β-nitronitriles in excellent yield (up to 93%) with good enantioselectivity (up to 99%). This newly developed catalytic protocol led to the efficient synthesis of useful but challenging chiral α,α′-disubstituted β-amino acids.

Enantioselective Strecker reaction of aldimines using potassium cyanide catalyzed by a recyclable macrocyclic V(V) salen complex

A chiral dimeric macrocyclic V(V) salen complex based on a chiral macrocyclic salen ligand derived from 1R, 2R-(−) diaminocyclohexane with trigol bisaldehyde was synthesized and evaluated as an efficient catalyst (5 mol%) for asymmetric addition of potassium cyanide and trimethylsilyl cyanide to various N-benzylimines at −20 °C. The dimeric chiral macrocyclic salen complex was found to be an efficient recyclable catalyst to give a high yield (91%) of α-aminonitrile and high chiral induction (ee up to 99%) in the case of 2-methoxy substituted N-benzylimines in 16 h. The catalytic system worked well with both organic and inorganic cyanide sources and the catalyst was recycled up to five cycles with retention of enantioselectivity. Based on NMR investigation and kinetics a probable mechanism was proposed for the catalytic enantioselective Strecker reaction.