Vipin A. Nair

Highly stereoselective furoindoline derivatives were synthesized by exploring the imidazolidinone‐based chiral auxiliary‐mediated aldol adduct. The one‐pot reductive cyclization was achieved through NiCl₂.6H₂O/NaBH₄.

Asymmetric Mannich‐type reaction employing 5‐isopropyl‐3‐phenyl‐2‐thioxoimidazolidin‐4‐one as a chiral auxiliary with various aldimines to obtain enantiomerically enriched β ‐amino carbonyl functionalities with good yields and high trans ‐diastereoselectivities has been described. In order to establish the stereochemical outcome of the reaction, the Mannich‐adduct was hydrolysed using LiOH/H ₂ O ₂ and subsequently cyclized with thionyl chloride to afford the corresponding β ‐lactam in good yield and high stereoselectivity.

Stereoselective total synthesis of Ligraminol E has been achieved in 8 steps in 23.9 % overall yield by employing an imidazolidinone based chiral auxiliary. The key steps involved in the synthesis are the asymmetric glycolate alkylation of ( R )‐3‐(2‐(benzyloxy)acetyl)‐4‐isopropyl‐1‐(( S )‐1‐phenylethyl)imidazo‐lidin‐2‐one with substituted benzyl bromide and the Mitsonobu reaction of a secondary alcohol and phenolic group.

The anti selective glycolate aldol reactions of (S)-4-isopropyl-1-[(R)-1-phenylethyl]imidazolidin-2-one auxiliary have been standardized with high yields and excellent diastereoselectivities on various substituted aryl, allyl and alkyl aldehydes. The optimized reaction conditions were employed for the stereoselective synthesis of oxyneolignans.

An efficient, eco-friendly, base free, one-pot, sequential protocol was developed for epoxide azidolysis and copper-catalyzed azide–alkyne cycloaddition using water as the solvent for the synthesis of 3-hydroxy-1-alkyl-3-[(4-aryl/alkyl-1H-1,2,3-triazol-1-yl)methyl]indolin-2-ones. The optimized reaction conditions have been generalized in the case of aromatic as well as aliphatic alkyne partners to afford good yields and high regioselectivity.

(S)‐4‐Isopropyl‐1‐[(R)‐1‐phenylethyl]imidazolidin‐2‐one was evaluated as a chiral auxiliary for asymmetric acetate and propionate Mannich‐type reactions, by generation of the titanium enolates, affording excellent yields and stereoselectivities. The application of the auxiliary was exemplified in the stereoselective synthesis of the β‐lactam antihyperlipidemic drug ezetimibe.

An efficient protocol was developed for the Friedel Crafts type thioarylation for the synthesis of aromatic/heteroaromaticthioamide derivatives from aryl isothiocyanates and electron rich aromatic/heteroaromatic molecules by employing the Lewis acid AlCl ₃ and the less hazardous solvent cyclohexane at 70°C. The developed protocol offers advantages over the previous methods such as use of stoichiometric amount of reactants/reagent, less toxic solvent, shorter reaction time and higher yields.

Spirocarbocyclic‐oxindole is priviledged scaffold in heterocyclic chemistry, which paved the attention of synthetic chemist due to generation of a new stereocenter. Numerous methodologies have been developed for spirooxindoles but very few methods are available for carbocyclic oxindoles. Most of the reported cycloaddition reactions are five membered rings instead of six membered rings, tethered with oxindole scaffold. Lewis acid catalysed Diels Alder reaction is a comparatively better approach to functionalize this unique scaffold. An efficient diastereoselective synthesis of spirocarbocyclic‐oxindoles with six membered cabocyclic backbone was achieved via ZrCl ₄ catalyzed [4+2] cycloaddition of α ‐ylideneoxindoles with dienes in good to excellent yields within a short span of time.

Zirconocene dichloride was found to be a highly efficient catalyst for the synthesis of multi-substituted pyrroles by a three-component, one-pot reaction.

A highly efficient and atom-economic methodology has been developed for the synthesis of 3-(arylethynyl)-3-hydroxyindolin-2-ones from isatins by C–H activation of arylacetylenes using a catalytic quantity of copper(I) iodide (5 mol%) and DBU (20 mol%) at 25 °C, affording the products in excellent yields in very short reaction time (5 min).