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Synlett 2013; 24(9): 1101-1104
DOI: 10.1055/s-0033-1338384
DOI: 10.1055/s-0033-1338384
letter
Efficient Synthesis of 2-Pyridylenynes and Application in Cobalt-Catalysed Benzannulation Reactions
Weitere Informationen
Publikationsverlauf
Received: 19. Februar 2013
Accepted after revision: 20. März 2013
Publikationsdatum:
23. April 2013 (online)
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Abstract
The cobalt-catalysed benzannulation of 2-pyridine-substituted enynes gave 2,3-bis(2-pyridyl)styrenes in moderate yields. The reaction with dibromomethane as well as diiodomethane generated the corresponding planar-chiral bispyridinium salts in good yields. On the other hand, the transformations with reagents of the type RCHBr2 to afford diastereomeric products led to the desired conversion. However, these products could not be obtained in pure form.
Supporting Information
- for this article is available online at http://www.thieme-connect.com/ejournals/toc/synlett.
- Supporting Information
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References and Notes
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- 4 General Procedure for the Stepwise Sonogashira Reaction of 2-Iodo- and 2-Bromopyridines of Type 4 PdCl2(PPh3)2 (42 mg, 2.0 mol%), CuI (11 mg, 2.0 mol%), and Ph3P (32 mg, 4.0 mol%) were suspended in toluene (10 mL). To the suspension, degassed i-Pr2NH (1.0 mL, 7.00 mmol, 2.3 equiv), 2-iodo- or 2-bromopyridine 4 (3.00 mmol, 1.0 equiv) and ethynyltrimethylsilane (0.5 mL, 3.60 mmol, 1.2 equiv) were added successively, and the reaction mixture was stirred at r.t. for 2 d. K2CO3 (2.90 g, 21.0 mmol, 7.0 equiv) and MeOH (20 mL) were added to the mixture and stirred at r.t. until complete conversion was observed by TLC or GC–MS analysis. The reaction mixture was concentrated under reduced pressure, H2O was added followed by extraction with CH2Cl2, and dried over Na2SO4. The crude product was purified by column chromatography to give the desired product 5 [the same procedure was used for the second Sonogashira reaction with vinyl bromide (1 M in THF, 1.2 equiv) instead of ethynyltrimethylsilane].
- 5 Severin R, Reimer J, Doye S. J. Org. Chem. 2010; 75: 3518
- 6 One-Pot Procedure for the Synthesis of 2-Pyridyl enynes of Type 6 PdCl2(PPh3)2 (42 mg, 2.0 mol%), CuI (11 mg, 2.0 mol%), and Ph3P (32 mg, 4.0 mol%) were suspended in THF (10 mL). To the suspension, degassed i-Pr2NH (1.0 mL, 7.00 mmol, 2.3 equiv), 2-iodo- or 2-bromopyridine 4 (3.00 mmol, 1.0 equiv), and ethynyltrimethylsilane (0.5 mL, 3.60 mmol, 1.2 equiv) were added successively, and the reaction mixture was stirred at r.t. for 2 d. KOH (1.18 g, 21.0 mmol, 7.0 equiv) in MeOH–H2O (15 mL, 4:1 v/v) were added to the mixture and stirred at r.t. for 3.5 h. Then vinyl bromide [3.6 mL (1 M in THF), 3.60 mmol, 1.2 equiv] were added and stirred at r.t. for another 16 h. The reaction mixture was concentrated under reduced pressure, H2O was added followed by extraction with CH2Cl2, and dried over Na2SO4. The crude product was purified by column chromatography to give the desired product 6.
- 7 General Procedure for the Cobalt-Catalysed Benzannulation Reaction of 2-Pyridyl Enynes of Type 6 CoBr2(dppp) (126 mg, 20 mol%), Zn powder (26 mg, 40 mol%), and ZnI2 (128 mg, 40 mol%) were dissolved in DMSO (1.5 mL), and the enynes of type 6 were added (1.00 mmol). The reaction mixture was stirred at r.t. until complete conversion was observed by TLC or GC–MS analysis. A solution of EDTA (584 mg, 2.00 mmol) in aq NH3 buffer (20 mL, pH 10) was added followed by extraction with CH2Cl2. The organic layers were combined, dried over Na2SO4, the solvent was evaporated, and the crude product was purified by column chromatography to give the desired styrene derivatives 7.
- 8 Almarzoqi B, George AV, Isaacs NS. Tetrahedron 1986; 42: 601
- 9 The supplementary crystallographic data can be obtained free of charge from The Cambridge Crystallographic Data Centre; CCDC 924471.
- 10 Representative Procedure for the Synthesis of the Bispyridinium Salt 8a CH2Br2 (20 μL, 0.29 mmol, 1.45 equiv) was added to a solution of 2,3-bis(2-pyridyl)styrene 7a (52 mg, 0.20 mmol, 1.0 equiv) in MeCN (1.0 mL) and was stirred at 70 °C for 3 d. The solvent was removed, the residue washed successively with 3.0 mL CH2Cl2, Et2O, and pentane and dried under reduced pressure to give the desired product 8a.