Phosphorus(III) Bromide-Copper(I) Bromide-Zinc


[7789-60-8]  · Br3P  · Phosphorus(III) Bromide-Copper(I) Bromide-Zinc  · (MW 270.67) (Cu2Br2)

[7787-70-4]  · Br2Cu2  · Phosphorus(III) Bromide-Copper(I) Bromide-Zinc  · (MW 286.90) (Zn)

[7440-66-6]  · Zn  · Phosphorus(III) Bromide-Copper(I) Bromide-Zinc  · (MW 65.39)

(conversion of enediols into 1,3-dienes)

Physical Data: see entries for Phosphorus(III) Bromide, Copper(I) Bromide, and Zinc.

General Discussion.

Transformation of 3-ene-1,2-diols into 1,3-dienes can be accomplished in the presence of PBr3 and Cu2Br2, followed by addition of excess Zn powder.1,2 Excess Cu2Br2 (2.5 equiv) is utilized for the best results. It is thought that the Cu2Br2 facilitates both bromination and debromination to afford the conjugated dienes. Treatment of the reaction with zinc should be monitored carefully, since longer reaction times can cause cyclization induced by the Zinc Bromide and reduce yields of the desired alkenes. A variety of dienes can be produced by this method. Overall, allylic alcohols can be transformed into 1,3-dienes (eq 1). First, the allylic alcohol is epoxidized using the Sharpless epoxidation procedure, followed by protection of the alcohol as the silyl ether. Conversion of the epoxy silyl ether into the 3-ene-1,2-diol can be accomplished by treatment with Diethylaluminum 2,2,6,6-Tetramethylpiperidide (DATMP). Deoxygenation using PBr3-Cu2Br2-Zn gives moderate yields of the diene. Deoxygenation using other standard methods gives low yields of alkene products. Geraniol can likewise be converted to the corresponding 1,3-diene (eq 2), and cyclic enediols can also be deoxygenated to afford cyclic dienes (eq 3).

Related Reagents.

Chlorodiphenylphosphine; Potassium Hexachlorotungstate(IV).

1. Tanaka, S.; Yasuda, A.; Yamamoto, H.; Nozaki, H. JACS 1975, 97, 3252.
2. Yasuda, A.; Tanaka, S.; Yamamoto, H.; Nozaki, H. BCJ 1979, 52, 1752.

Suzanne M. Ruder

Virginia Commonwealth University, Richmond, VA, USA

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