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Azomethine Ylides from Nitrones: Using Catalytic n BuLi for the Totally Stereoselective Synthesis of trans ‐2‐Alkyl‐3‐oxazolines
Author(s) -
JusteNavarro Veronica,
Delso Ignacio,
Tejero Tomás,
Merino Pedro
Publication year - 2016
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201602159
Subject(s) - chemistry , catalysis , moiety , stereoselectivity , nitrone , cycloaddition , medicinal chemistry , aldehyde , ylide , catalytic cycle , butyllithium , lithium (medication) , nucleophile , alkyl , organic chemistry , medicine , endocrinology
The cycloaddition of azomethine ylide N ‐oxides (nitrone ylides) with aldehydes provides 3‐oxazolines in a completely stereoselective manner in the presence of a catalytic amount of n ‐butyllithium. The process involves an initial nucleophilic attack on the aldehyde, followed by intramolecular oxygen addition to the nitrone moiety and lithium‐assisted elimination of water, regenerating the catalytic species. Various Li‐based catalytic systems are possible and the in situ generated water is required for continuing the catalytic cycle. The best results are observed with 20 mol % of n ‐butyllithium, whereas the use of stoichiometric amounts inhibit the rate of catalysis. Experimental, spectroscopic, and computational mechanistic studies have provided evidence of lithium‐ion catalysis and rationalized several competing catalytic pathways