Biomedical Engineering Reference
In-Depth Information
(a)
(b)
(c)
SCHEME 2.14
Ugi Diels-Alder methodology.
resulting in isoindolinone products (Scheme 2.14b) [42]. Similar products result from
treating the oxabicyclic intermediates
96
with a Lewis acid to induce ring opening
and aromatization (Scheme 2.14c) [43].
Heterocycles may be formed from inverse electron-demand Diels-Alder reactions.
Propargyl amine and heterocyclic acid
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undergo the Ugi 4CR, and the resulting
bicyclic intermediate (not shown) spontaneously loses molecular nitrogen to pro-
duce substituted pyridine products (Scheme 2.15a) [44]. Sun et al. observed a related
process after a 3CR in which the nitrilium ion intermediate of the Ugi reaction is
trapped to form oxazole
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[45]. This intermediate could be acylated with an unsatu-
rated acid chloride to form substrates for an intramolecular Diels-Alder reaction that
