A simple and metal-free method for the synthesis of a series oftrans-4-arylchroman-3-olsviaBrønsted acid-catalysed stereoselective intramolecular Friedel–Crafts alkylation of electron-rich arenes by tethered epoxides is developed.

Am etal-free and catalytic methodf or the synthesis of 2-substitutedb enzoxazoles and benzothiazoles from N-protecteda mino acids and carboxylic acids is described. The synthesis of benzoxazole on as olid support is demonstrated by the synthesis of benzoxazole attached to ah uman islet amyloid polypeptide, hIAPP [22][23][24][25][26][27] ,f ragment and benzoxazole derivatives of the side chain of aspartic acido n am odified fragment of Ab 18À21 (amyloid b)p eptide. The reactions proceeded through at wo-step mechanism.T he coupling step is realized with ar elativelyn ew reagent, ethyl 2-cyano-2-(2-nitrobenzenesulfonyloxyimino)acetate (ortho-NosylOXY), and the cyclization step takes place thanks to an inexpensive organocatalyst, para-toluenesulfonic acid, under microwavei rradiation. To the best of our knowledge,t his is the first report of the complete synthesis of benzoxazole derivatives of ap olypeptide on aresin solid support.

An efficient, convenient, and selective Lewis acid-based strategy for on-resin deprotection of the side chain tert -butyl-protected aspartic acid and glutamic acid of a peptide is achieved. The method is mild, cost-effective, and Fmoc chemistry compatible and allows on-resin incorporation of amides, esters, and thioesters in good yield. This method will find wide applicability in peptide and protein modification because it enriches the toolbox of orthogonal protection/deprotection techniques.

We demonstrate a simple and effective methodology for acetalization and thioacetalization of aldehydes by catalytic amount of ethyl-2-cyano-2-(2-nitrophenylsulfonyloximino) acetate (ortho-NosylOXY), a novel peptide coupling reagent. This safe reagent successfully transforms the aldehydes into cyclic acetals, 1,3-dithiolanes, and 1,3-dithianes. The reaction is compatible with electron-withdrawing and donating substituents containing aldehydes and different kinds of diols and dithiols. Also, the reaction worked well with an α,β-unsaturated aldehyde, and an aliphatic aldehyde. Yields are impressive (71 to 95 %) at a moderate temperature and short time. Hence, broad substrate scope, high yield, easy isolation of the products, and catalytic nature of the reagent make this methodology an environment-friendly alternative to the existing ones.

A method for Beckmann rearrangement using ethyl 2‐cyano‐2‐(2‐nitrobenzenesulfonyloxyimino) acetate (o‐NosylOXY) under microwave irradiation is reported. Ketoximes (19 examples) are converted to the corresponding amides/lactams with 69–97% yields in ∼10 minutes without any Lewis acid or co‐catalyst. This is an example of halogen‐free organocatalytic Beckmann rearrangement. Nuclear magnetic resonance (NMR)‐ and high‐resolution mass spectrometry (HRMS)‐based detailed mechanistic investigation suggest that o‐NosylOXY acts as an initiator. Such initiators are reported before based on density functional theory (DFT) calculations. However, we report here the HRMS signatures of two transient intermediates, the nitrilium ion and the nitrilium ion's dimeric species. Rigorous NMR‐based investigation of the reaction mechanism is performed. Our results indicate that the reported Beckmann rearrangement proceeds via two consecutive rearrangements.