Catalytic Synthesis of Coumarins
via Direct Annulations of α,β-Unsaturated Aldehydes
and Salicylaldehydes

Ulrike Gross; Patrick J. Gross; Min Shi; Stefan Bräse

doi:10.1055/s-0030-1259691

LETTER

Catalytic Synthesis of Coumarins via Direct Annulations of α,β-Unsaturated Aldehydes and Salicylaldehydes

Ulrike Gross^a,b, Patrick J. Gross^a,b, Min Shi*^b, Stefan Bräse*^a
^a Institute of Organic Chemistry, Karlsruhe Institute of Technology (KIT), Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany
e-Mail: stefan.braese@kit.edu;
^b State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry (SIOC), Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai 200032, P. R. of China
e-Mail: mshi@mail.sioc.ac.cn;

Abstract

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Abstract

The first organocatalytic approach towards substituted coumarins is reported. Catalytic amounts of in situ generated N-heterocyclic carbenes (NHC) catalyze a one-pot redox esterification of α,β-unsaturated aldehydes with simultaneous aldol condensation.

Key words

domino reactions - heterocycles - umpolung

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References

References and Notes

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Typical Procedure
To a round-bottom flask with reflux condenser under argon atmosphere were added salicylaldehyde (20 µL, 23 mg, 0.19 mmol), crotonaldehyde (23 µL, 19 mg, 0.28 mmol, 1.5 equiv), 1,3-diisopropyl-imidazolium chloride (7.0 mg, 37 µmol, 20 mol%), Cs₂CO₃ (60 mg, 0.19 mmol, 1.0 equiv) and o-xylene (1.0 mL). The reaction mixture was heated to 120 ˚C for 12 h. Then H₂O (10 mL) was added, and the resulting mixture was extracted with EtOAc (3 × 10 mL). The combined organic extracts were washed with brine (10 ml), dried over MgSO₄, and evaporated under reduced pressure. Purification by chromatography on silica gel, eluting with PE-EtOAc (20:1), yielded the desired product 4ac (26 mg, 81%) as a pale yellow solid.

Supplementary Material

Supporting Information