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Synlett 2012(6): 907-912  
DOI: 10.1055/s-0031-1290618
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

A Convenient Solid-Phase Synthesis of Coumarins by TMSOTf-Catalyzed Intramolecular Seleno-Arylation of Tethered Alkenes

E. Tang*a,b, Wen Lib, Zhangyong Gaob
a Key Laboratory of Medicinal Chemistry of Natural Resource (Yunnan University), Ministry of Education, P. R. of China
b School of Chemical Science and Technology, Yunnan University, No 2 Green Lake North Road, Kunming 650091, P. R. of China
Fax: +86(871)5033725; e-Mail: tange@ynu.edu.cn;
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Publication History

Received 12 December 2011
Publication Date:
15 March 2012 (online)

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Abstract

TMSOTf-catalyzed intramolecular seleno-arylation of tethered alkenes was performed using polystyrene-supported succinimidyl selenide as the selenium source. This catalytic process provides an efficient method for the regioselective synthesis of dihydrocoumarins possessing a seleno functionality, followed by syn elimination of selenoxides to provide coumarins in good yields and purities. Suzuki cross-coupling reaction of the resin-bound bromodihydrocoumarin was also performed, and biphenyl coumarin was obtained by subsequent cleavage of selenium linker.

Key words

selenium - cyclization - TMSOTf - coumarins - solid-phase synthesis - carbon-carbon bond formation - catalysis

27

Typical Procedure for the Preparation of Polystyrene-Supported Allyl Selenide (2)
To a suspension of the swollen polystyrene-supported selenenyl bromide (1, Br: 0.99 mmol/g, 2.5 g) in dry THF-DMF (v/v = 5:1, 30 mL) was added NaBH4 (5 mmol) under nitrogen atmosphere at 40 ˚C. After stirring for 8 h at 40 ˚C, 3-bromoprop-1-ene (5.5 mmol) was added dropwise under nitrogen atmosphere, and stirred for another 12 h. The resin 2 was collected by filtration, washed with THF (2 × 20 mL), MeOH (2 × 20 mL), and CH2Cl2 (2 × 20 mL), and dried in vacuum.

28

Typical Procedure for the Preparation of 6-Methyl-4-phenyl-3-(phenylselenyl)-2 H -chromen-2-one [(±)-6]
To an oven-dried flask (25 mL) was added polystyrene-supported succinimidyl selenide (PSSS, 0.27 g, 1.05 mmol) in dry CH2Cl2 (10 mL) under nitrogen atmosphere, and the solution was cooled at -78 ˚C. Trimethylsilyl trifluoro-methanesulfonate (TMSOTf, 0.022 g, 0.1 mmol) was added. After stirring for 0.5 h at -78 ˚C, p-tolyl cinnamate (0.238 g, 1.0 mmol) was added under nitrogen atmosphere. The mixture was stirred for another 2 h at -78 ˚C and then stored in a freezer at -20 ˚C for 8 h. Saturated aq NaHCO3 (5 mL) was poured into the flask to quench reaction mixture. The organic phase was separated, and the aqueous phase was extracted with fresh portion of CH2Cl2 (25 mL). The extracts were combined, washed with H2O, and dried over MgSO4. After filtering and concentrating under reduced pressure by rotary evaporation at r.t, the oily residue was subjected to preparative TLC on silica gel with EtOAc-light PE (1:9) as eluent to give 197 mg of (±)-6 (50% isolated yield).

29

General Procedure for the Preparation of 2 H -Chromen-2-one (5)
To a suspension of the swollen resin 2 (1.0 g) in dry CH2Cl2 (15 mL) was added NCS (0.668 g, 5.0 mmol) at 0 ˚C. The mixture was stirred for 0.5 h at 0 ˚C and 2 h at r.t. After filtrating and washing with dry CH2Cl2 (3 × 15 mL), PSSS was suspended with dry CH2Cl2 (15 mL) and cooled to -78 ˚C. TMSOTf (0.022 g, 0.10 mmol) was added. After stirring for 0.5 h at -78 ˚C, substituted phenyl acrylate 3 (5.0 mmol) was added under nitrogen atmosphere. The suspension was stirred for another 2 h at -78 ˚C and then stored in a freezer at -20 ˚C for 8 h. Saturated aq NaHCO3 (5 mL) was poured into the flask to quench the reaction mixture. 3-Polystyrene-supported seleno-3,4-2H-chromen-2-one [(±)-4] was collected by filtration, washed with THF (2 × 20 mL), Et2O (2 × 20 mL), THF-H2O (3:1, 2 × 20 mL), H2O (2 × 20 mL), THF (2 × 20 mL), benzene (2 × 20 mL), MeOH (2 × 20 mL), and CH2Cl2 (2 × 20 mL), and dried under vacuum. The washed resin (±)-4 was suspended in THF (15 mL). To the mixture was added 30% aq H2O2 (1.2 mL). The mixture was stirred for 1 h at 0 ˚C and then for another 20 min at r.t. The mixture was filtered, and the resin was washed with CH2Cl2 (2 × 15 mL). The filtrate was washed with H2O (2 × 30 mL), dried over MgSO4, and evaporated to dryness in vacuum to afford 2H-chromen-2-ones 5.

30

Typical Procedure for the Preparation of 4-Biphenyl-2 H -chromen-2-one (10)
To a suspension of the swollen resin (±)-4d (0.5 g) in dry THF (15 mL) was added Pd(OAc)2 (0.0056 g, 0.025 mmol), phenylboronic acid (0.61 g, 5.0 mmol), KF (0.58 g, 10.0 mmol), and 2-(dicyclohexylphosphino)biphenyl [o-(biphenyl)PCy2] (0.175 g, 0.5 mmol) under a nitrogen atmosphere. The reaction mixture was stirred at r.t. for 24 h. Resin (±)-9 was collected by filtration, washed with THF (2 × 20 mL), Et2O (2 × 20 mL), THF-H2O (3:1, 2 × 20 mL), H2O (2 × 20 mL), THF (2 × 20 mL), benzene (2 × 20 mL), MeOH (2 × 20 mL), and CH2Cl2 (2 × 20 mL), and dried in vacuum. The washed resin (±)-9 was suspended in THF (15 mL). To the mixture was added 30% aq H2O2 (1.5 mL) and stirred for 1.5 h at 0 ˚C, and stirred for another 20 min at r.t. The mixture was filtered, and the resin was washed with CH2Cl2 (2 × 15 mL). The filtrate was washed with H2O (2 × 30 mL), dried over MgSO4, and evaporated to dryness under vacuum to afford 4-biphenyl-2H-chromen-2-one (10).

31

6-Methyl-4-phenyl-3-(phenylselenyl)-2 H -chromen-2-one [(±)-6]
Yellow oil. ¹H NMR (400 MHz, CDCl3): δ = 7.35-7.07 (11 H, m), 6.86 (2 H, dt, J 1 = 8.4 Hz, J 2 = 2.8 Hz), 4.58 (1 H, d, J = 10.8 Hz), 4.04 (1 H, d, J = 10.4 Hz), 2.33 (3 H, s). ¹³C NMR (100 MHz, CDCl3): δ = 170.10, 148.59, 135.90, 135.65, 135.47, 129.97, 129.07, 128.96, 128.78, 128.54, 128.44, 127.79, 121.12, 79.10, 51.07, 20.96. IR (KBr): ν = 1741, 1496, 1431, 1208, 1010, 736, 693 cm-¹. HRMS:
m/z [M]+ calcd for C22H18O2Se: 394.0472; found: 394.0470.