Multicomponent Coupling Reaction and Intramolecular Nitrile Oxide–Alkyne Cycloaddition towards Isoxazolo [3, 4]‐pyrrolizines

SN Afraj, C Nuzlia, C Chen… - Asian Journal of Organic …, 2016 - Wiley Online Library
SN Afraj, C Nuzlia, C Chen, GH Lee
Asian Journal of Organic Chemistry, 2016Wiley Online Library
This study reports an efficient four‐step method to synthesize a series of new (4S, 8aS)‐3, 4‐
diphenyl‐6, 7, 8, 8a‐tetrahydro‐4H‐isoxazolo [3, 4‐a] pyrrolizines. The first step involves a
copper (II) acetylacetonate catalyzed three component coupling of aldehyde,(S)‐pyrrolidin‐2‐
ylmethanol, and alkynes (A3 coupling) to form propargylamines (4 a–4 n). The coupling
reaction is applicable to various aldehydes, amines, and alkynes and provides the
propargylamines in good to excellent yields with excellent distereoselectivities. Products (4 …
Abstract
This study reports an efficient four‐step method to synthesize a series of new (4S,8aS)‐3,4‐diphenyl‐6,7,8,8a‐tetrahydro‐4H‐isoxazolo[3,4‐a]pyrrolizines. The first step involves a copper(II) acetylacetonate catalyzed three component coupling of aldehyde, (S)‐pyrrolidin‐2‐ylmethanol, and alkynes (A3 coupling) to form propargylamines (4 a4 n). The coupling reaction is applicable to various aldehydes, amines, and alkynes and provides the propargylamines in good to excellent yields with excellent distereoselectivities. Products (4 a4 n) were converted into aldehydes (5 a5 n) by Swern oxidation, aldehydes (5 a5 n) were reacted with hydroxyl amine hydrochloride to form aldoxime (6 a6 n), respectively. Further aldoximes (6 a6 n) underwent an intramolecular 1,3‐dipolar cycloaddition to form tricyclic‐fused isoxazoles (7 a7 n). The 1,3‐dipolar cycloaddition reaction tolerates high structural diversity and generated desired products (7 a7 n) in moderate to good yields and excellent diastereoselectivities. A proposed mechanism for synthesis of 7 a is reported.
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