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Synlett 2005(6): 1009-1011
DOI: 10.1055/s-2005-864817
DOI: 10.1055/s-2005-864817
LETTER
© Georg Thieme Verlag Stuttgart · New York
Petasis Boronic Mannich Reactions of Electron-Poor Aromatic Amines under Microwave Conditions
Further Information
Received
22 December 2004
Publication Date:
23 March 2005 (online)
Publication History
Publication Date:
23 March 2005 (online)
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Abstract
The Petasis reaction of electron-poor aromatic amines such as aminopyridines under microwave irradiation conditions is described. The process provides rapid access to a number of unnatural N-aryl-α-amino acids. The influence of the electronic demand of the boronic acids on the yields is discussed. A comparison with conventional heating is provided.
Key words
amino acids - boron - green chemistry - heterocycles - multicomponent reactions
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General Procedure of (4-Methoxyphenyl)-(pyridin-3-ylamino) Acetic Acid (7b).
3-Aminopyridine (5, 23.5 mg, 0.25 mmol), 4-methoxy phenyl boronic acid (6b, 38 mg, 0.25 mmol) and 1.2 equiv glyoxylic acid monohydrate (28 mg, 0.30 mmol) were suspended in 2 mL MeCN and 0.2 mL DMF. The slurry was heated in a capped microwave vial using magnetic stirring for 5 min at 120 °C (300 W, method A) or heated in a screw cap vial under stirring for 0.5-4 h in a preheated aluminum block (method B). After cooling down to r.t. the liquid was filtered and injected in a preparative HPLC system without any further workup. The fractions containing product were freeze-dried yielding 70 mg (87%) of a colorless foam. ESI+: m/z calcd for C14H14N2O3 [M+]: 258.1004; found: 259.1077 [M + H]+). 1H NMR [500 MHz, (CD3)2SO]: δ = 5.33 (1 H, d, J = 4.9 Hz, NCH), 6.95 (2 H, d, J = 8.6 Hz, phenyl), 7.40 (2 H, d, J = 8.6 Hz, phenyl), 7.69 (2 H, m, pyridine), 8.04 (1 H, br dd, J = 4.3, 1.9 Hz, pyridine), 8.15 (1 H, br s, pyridine)
References
Microwave system employed: Personal Chemistry’s Emrys Optimizer. See: www.biotage.com.