Efficient and Atom-Economic
Synthesis of α-Substituted β-Chromonyl-α,β-unsaturated
Carbonyls through Molecular Rearrangement
Vivek Khedkara, Wei Liua,b, Heiko Dückerta,b, Kamal Kumar*a a Max Planck Institut für Molekulare
Physiologie, Otto-Hahn Str. 11, 44227 Dortmund, Germany Fax: +49(231)1332496; e-Mail: Kamal.Kumar@mpi-dortmund.mpg.de; b Technische Universität Dortmund, Fachbereich Chemie, 44221 Dortmund,
Germany
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Publikationsverlauf
Received
23 October 2009 Publikationsdatum: 07. Januar 2010 (online)
Under mild acidic conditions [4+2] cycloadducts
of 3-formylchromones and acetylenecarboxylates rearrange to yield α-substituted-β-chromonyl-α,β-unsaturated
carbonyl compounds in excellent yields.
1fFerreira D.
Slade D.
Marais JPJ. In Flavonoids: Chemistry, Biochemistry
and ApplicationsAndersen OM.
Markham KR.
CRC Press;
Boca
Raton:
2006.
p.553-616
General Procedure
for the Rearrangement of the Adducts 3 to 4 TFA (1
mL in 5 mL CH2Cl2) was added slowly dropwise
to the CH2Cl2 solution (5 mL) of the tricyclic
benzopyrones 3 (1 mmol). The reaction mixture
was stirred at r.t. for 30 min under argon. The reaction was monitored
by TLC using cyclohexane-EtOAc (7:3) as eluent. After evaporation
of the solvent, the crude product was purified by column chroma-tography
on silica gel with cyclohexane-EtOAc as the eluent.
An alternative synthesis of 4 by a Wittig olefination of 3-formylchromone
would require the corresponding ketoester or aldehydic phosphoranes
which are not commercially available and require multistep synthesis
and also remain susceptible to self-olefination and polymerization
reaction. The same is true for the alternative aldol condensation strategy
to provide 4 by reacting chromone aldehydes
with ketoester 7. Using our previously
reported methodology¹4 to condense 1,3-dicarbonyls
with 3-formylchromone, we could observe self-condensation products
of 7 but not any formation of 4a (Scheme
[4]
).
