Iodine(III)-Mediated Keto-oximation of O-Alkynyl Hydroxylamines: A Route to 3-Acyl Isoxazolines and 1,2-Oxazines

MsOH Promoted Divergent Synthesis of 4-Arylidene Isoxazolidines and Isoxazolines from O-Propargyl Hydroxylamines and Aldehydes

Temperature-dependent, Brønsted-acid-mediated divergent synthesis of 4-arylidene isoxazolidines and isoxazolines from O-propargyl hydroxylamines is developed. A series of control and crossover experiments have been carried out, revealing that the formation of 4-arylidene isoxazoline proceeds through an alkyne-oximium cyclization, ring-opening reaction, and subsequent condensation. Synthetic versatility of the developed methodology was highlighted in the synthesis of 3-aminoacrylaldehyde, β-hydroxy ketone, and isoxazole derivatives.

BF3·OEt2 Mediated Stereoselective Synthesis of 1,2-Heterocycle Fused Isoindolone Derivatives via Intramolecular Alkyne Oximium Cyclization of Oxoisoindolidene

In this research we report Lewis acid mediated intramolecular alkyne oximium cyclization cascade on oxoisoindolidene for the stereoselective syntheses of isoxazolidine/oxazinane/oxazepane fused isoindolones bearing three chiral centers. The approach enables the construction of a new C-C and C-O bonds along with an aza-tertiary stereocenter. The developed protocol features a wide range of substrate scope, functional group tolerance, and has been utilized in the synthesis of tetracyclic lactone.

Alkynyl hydroxylamines: key precursors for 1,2-N/O heterocycles

1,2-N/O Heterocycles are privileged scaffolds found in numerous natural products and have been shown to exhibit diverse pharmacological properties. Additionally, these compounds have emerged as important synthons in organic chemistry. Recent years have witnessed immense interest in these heterocycles from both the medicinal and the synthetic chemistry community. In light of the ever-increasing demand for isoxazolidine, isoxazoline, isoxazole, 1,2-oxazinane, 1,2-oxazine and 1,2-oxazepine in drug discovery, this review highlights an overview of recent methods (up to 2024) for the synthesis of these heterocycles starting from alkynyl hydroxylamines. The mechanistic pathways and stereo-electronic factors affecting yield and selectivity of the products are briefly explained to generate the understanding needed for future developments in this domain.