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Synlett 2010(10): 1539-1543  
DOI: 10.1055/s-0029-1219926
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

A Multi-Task Palladium Catalyst Involved in Heck-Reduction-Cyclization Sequences for the Preparation of 4-Benzyl-1,2-dihydroisoquinolin-3-ones: An Unusual Homogeneous-Heterogeneous Sustainable Approach

Julia Laudiena, Eric Fouqueta, Cécile Zakrib, François-Xavier Felpin*a
a Université de Bordeaux, UMR CNRS 5255, Institut des Sciences Moléculaires, 351 Cours de la Libération, Talence 33405, France
Fax: +33(5)40006286; e-Mail: fx.felpin@ism.u-bordeaux1.fr;
b Université de Bordeaux, CNRS, Centre de Recherche Paul Pascal, Avenue Schweitzer, 33600 Pessac, France
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Publication History

Received 16 March 2010
Publication Date:
10 May 2010 (online)

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Abstract

A mixed homogeneous-heterogeneous catalysis that exploits a multi-task palladium catalyst has been developed for one-pot sequential Heck-reduction-cyclization (HRC) reactions leading to novel 4-benzyl-1,2-dihydroisoquinolin-3-ones. The HRC sequence requires mild conditions and allows the separation of the palladium residues under the form of an in situ generated Pd(0)/C catalyst by simple filtration. The homemade and recovered catalyst can be efficiently reused for Suzuki-Miyaura reactions and reductive processes making it useful for sustainable chemistry.

Key words

heterogeneous catalysis - heterocycles - palladium - Heck reaction - hydrogenation

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General Procedure for the Cyanation of Iodoaryls 7a,b: To a solution of iodoaryl 7a,b (7.00 mmol, 1 equiv) in DMF (7 mL) was added CuCN (689 mg, 7.7 mmol). The resulting mixture was stirred for 4-5 h at 130 ˚C and then filtered. The solution was diluted with CH2Cl2 (21 mL) and hydrolyzed with 5% aq NH4OH solution. After being stirred for 30 min, the aqueous layer was extracted with CH2Cl2 (3 ×). The collected organic extracts were dried (MgSO4) and concentrated under reduced pressure. Purification by flash chromatography gave the expected products 8a,b.

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General Procedure for the Preparation of Acrylates 1a,b: To a solution of ester 8a,b (10 mmol, 1 equiv) in toluene (13 mL) were added HCHO (28 mmol, 2.8 equiv), Bu4NI (0.2 mmol, 0.04 equiv) and K2CO3 (30 mmol, 3 equiv) at r.t. The resulting mixture was stirred for 5 h at 50 ˚C. After cooling to r.t., H2O (10 mL) was added and the aqueous phase was extracted with toluene (2 × 20 mL). The collected organic extracts were dried (MgSO4), filtered and concentrated under reduced pressure to give the corresponding products 1a,b which were purified by flash chromatography.

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General Procedure for the Preparation of 4-Benzyl-1,2-dihydroisoquinolin-3-ones 5a-h: Acrylate 1a,b (1 mmol) and Pd(OAc)2 (5 mol%) were added to a solution of diazonium salt (1.2 mmol) in MeOH (5 mL). The reaction was stirred for 12 h at 40 ˚C, charcoal (110 mg) was added and the resulting mixture was stirred under H2 (balloon, 1 atm) for 24 h at 50 ˚C. After cooling to r.t., K2CO3 (2 mmol) was added in one portion and the heterogeneous mixture was stirred for 2 h, filtered, and purified by flash chromatography to give the corresponding 4-benzyl-1,2-dihydroisoquinolin-3-ones 5a-h.