Cobalt-Catalyzed Regio- and Stereoselective Allylzincation of 1-Phenyl-1-alkynes

Abstract

The cobalt-catalyzed allylzincation reaction of 1-phenyl-1-alkynes proceeds with high regio- and stereoselectivity. The resultant alkenylzinc species undergo further functionalization upon treatment with electrophiles.

Key words

alkynes - allylzincation - cobalt

References

• For reviews on carbometalation, see:
• 1a Normant JF. Alexakis A. Synthesis  1981,  841 
• 1b Oppolzer W. Angew. Chem., Int. Ed. Engl.  1989,  28:  38 
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• 3 It was reported that dialkylzinc and diphenylzinc reagents in the presence of catalytic amount of Ni(acac)₂ add to internal alkynes with regio- and stereoselectivity: Stüdemann T. Knochel P. Angew. Chem., Int. Ed. Engl.  1997,  36:  93 
• 4 Allylzincation of 1-trimethylsilyl-1-alkyne with 2-(alkoxymethyl)-2-propenylzinc bromide was reported: van der Louw J. van der Baan JL. Bickelhaupt F. Klumpp GW. Tetrahedron Lett.  1987,  28:  2889 

5

General Procedure: The allylzincation followed by trapping with allyl bromide is representative. A solution of allylzinc bromide (1.50 mL, 1.34 M THF solution, 2.0 mmol) was added to a THF solution of CoCl₂ (3.2 mg, 0.025 mmol) and 1f (161 mg, 0.500 mmol) at r.t. The mixture was stirred for 48 h at r.t. To the mixture were added sequentially allylbromide (0.22 mL, 2.5 mmol) and CuCN·2LiCl (0.1 mL, 1.0 M THF solution, 0.1 mmol). After stirring for another 3 h, the mixture was poured into 1 M HCl and extracted with Et₂O (3 × 20 mL). The combined organic layer was dried and concentrated. Purification by silica gel column chromatography afforded 7 (142 mg, 0.35 mmol) in 70% yield.