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Synlett 2010(17): 2672-2676  
DOI: 10.1055/s-0030-1258571
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Palladium-Catalyzed, Microwave-Enhanced Three-Component Synthesis of Isoquinolines with Aqueous Ammonia

Monica Dell’Acqua, Giorgio Abbiati*, Elisabetta Rossi
Dipartimento di Scienze Molecolari Applicate ai Biosistemi (DISMAB) - Sezione di Chimica Organica ‘A. Marchesini’, Università degli Studi di Milano, Via G. Venezian 21, 20133 Milano, Italy
Fax: +39(02)50314476; e-Mail: giorgio.abbiati@unimi.it;
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Publication History

Received 2 August 2010
Publication Date:
23 September 2010 (online)

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Abstract

A variety of substituted isoquinoline derivatives can be synthesized in moderate yield by a palladium-catalyzed, microwave-assisted MCR starting from o-bromoarylaldehydes, terminal alkynes, and aqueous ammonia.

Key words

multicomponent reaction - alkynes - aqueous ammonia - isoquinoline - palladium

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Synthesis of 3-(4-Methoxyphenyl)isoquinoline (3d)
In a sealed MW test tube, to a solution of 2-bromobenz-aldehyde (1a, 185 mg, 0.116 mL, 1 mmol) in THF (1 mL), 4-ethynylanisole (159 mg, 0.156 mL, 1.2 mmol), and trans-dichlorobis(triphenylphosphine)palladium (7.02 mg, 0.01 mmol) were added. The solution was stirred at r.t. for 10 min, then NH3 (2.5 M aq, 3 mL) and CuI (3.81 mg, 0.02 mmol) were added. The stirred reaction mixture was heated at 130 ˚C (max. power setting = 500 W) in a multimode microwave oven (Microsinth Milestone®) for 2 h. The reaction mixture was diluted with H2O (70 mL) and extracted with EtOAc (3 × 70 mL). The organic layer dried with Na2SO4, was evaporated to dryness, and the crude material was purified by flash chromatography over a silica gel column (hexane-EtOAc = 96:4) yielding the isoquinoline 3d (132 mg, 56%) as brown solid; mp 85-87 ˚C. IR (KBr): 1626, 1606, 1584, 1512, 1447, 1292, 1249, 1179, 1024, 834 cm-¹. ¹H NMR (200 MHz, CDCl3): δ = 3.88 (s, 3 H, CH3), 7.04 (d, 2 H, arom, J = 8.8 Hz), 7.57 (ddd, 1 H, arom, J = 8.1, 7.0, 1.1 Hz), 7.67 (ddd, 1 H, arom, J = 8.4, 7.0, 1.5 Hz), 7.85 (d, 1 H, arom, J = 8.1 Hz), 7.95-7.99 (m, 2 H, arom), 8.08 (d, 2 H, arom, J = 8.8 Hz), 9.31 (s, 1 H, arom). ¹³C NMR (50.3 MHz, CDCl3): δ = 55.6 (CH3), 114.5, 115.5, 126.8, 126.9, 127.8, 128.4, 130.6, 152.5 (CH arom), 127.7, 132.6, 137.0, 151.4, 160.5 (C quat.). ESI-MS: m/z (%) = 236 (100) [M + 1]+. Anal. Calcd for C16H13NO (235.28): C, 81.68; H, 5.57; N, 5.95. Found: C, 81.77; H, 5.60; N, 5.93.