Synlett 2010(10): 1463-1468  
DOI: 10.1055/s-0029-1220070
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Palladium-Catalyzed Intramolecular C-H Activation: A Synthetic Approach towards Polycyclic Aromatic Hydrocarbons

Sunanda Paul, Rathin Jana, Jayanta K. Ray*
Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, India
e-Mail: jkray@chem.iitkgp.ernet.in;
Further Information

Publication History

Received 1 February 2010
Publication Date:
25 May 2010 (online)

Abstract

A simple and convenient synthetic protocol for the construction of polycyclic aromatic hydrocarbons has been developed. A variety of phenanthrene, benzo[c]phenanthrene and chrysene derivatives was synthesized via Pd-catalyzed intramolecular C-H activation followed by acid-catalyzed water elimination.

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General Procedure for the Grignard Reaction
Benzyl chloride (1.4 mmol) in anhyd Et2O (3 mL) was added dropwise with constant stirring to a suspension of magnesium turnings (4.3 mmol) in anhyd Et2O (4 mL). The mixture was refluxed on a warm water bath for 10 min to initiate the formation of Grignard reagent and then was stirred at r.t. for 1 h. The Grignard reagent was then added dropwise to the o-bromoaromatic aldehyde (0.8 mmol) in anhyd Et2O (5 mL) at 0 ˚C, and the mixture was stirred at that temperature for 30 min. The reaction was quenched with sat. aq NH4Cl solution, and the aqueous phase was extracted with Et2O (3 × 15 mL). The combined organic phases were washed with brine, dried over anhyd Na2SO4, filtered, and evaporated to give the crude product which was purified by silica gel (60-120 mesh) column chromatography using PE-EtOAc as the eluent.

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General Procedure for Pd-Catalyzed C-H Activation The precursor (1 mmol) and dry NaOAc (1.5 mmol) were flushed with argon and DMA (5 mL) was added to it. After degasification, Pd(PPh3)2Cl2 (5 mol%) was added, and the reaction mixture was heated at 130-140 ˚C for 2 h. This was then cooled and stirred with 2-3 mL of 6 N HCl for 5-10 min at r.t. The mixture was diluted with H2O and extracted with EtOAc (3 × 15 mL). After drying over anhyd Na2SO4 and filtering, the solvent was evaporated in vacuo to give the crude product which was purified by silica gel (60-120 mesh) column chromatography using PE as the eluent.