1,3-Butadienyl-1-magnesium Chloride

[114073-55-1]  · C4H5ClMg  · 1,3-Butadienyl-1-magnesium Chloride  · (MW 112.84) (E)

[112564-81-5] (Z)


(reagent for single-step introduction of the terminal 1,3-butadienyl group to various organic skeletons)

Solubility: sol THF, dioxane, DMF, 1,2-diethoxyethane, diethylene glycol dimethyl or diethyl ether, as well as in combinations of these solvents with aliphatic (n-hexane, n-octane) or aromatic (benzene, xylene) hydrocarbons.1

Preparative Method: 2,3 a mixture of Magnesium (24 g, 1.0 mol) and zinc chloride (6.8 g, 0.05 mol) was dried at 130 °C for 2 h under vacuum. Dried THF (30 mL) and 1,2-Dibromoethane (2.0 mL) were added and the mixture was stirred vigorously under an argon atmosphere. After the exothermic reaction had subsided, the reaction mixture was diluted by additional THF (350 mL), and then a solution of 1-chloro-1,3-butadiene (44 g, 0.5 mol) and 1,2-dibromoethane (4 mL) in THF (70 mL) was added dropwise over 1 h and the mixture was heated under reflux for 2 h. The concentration of the reagent solution is determined4 by titration using 1,10-phenanthroline as indicator. The average yield of 1,3-butadienyl-1-magnesium chloride was about 70%.

Handling, Storage, and Precautions: the reagent is moisture sensitive. Solvents must be carefully dried before use, and the preparation and reactions should be carried out under nitrogen or argon atmosphere.

Addition to Carbonyl Compounds.

Treatment of ketones or aldehydes with 1,3-butadienyl-1-magnesium chloride after hydrolytic work-up gave excellent yields of alcohols containing the 1,3-butadienyl group: 80-98% for aldehydes and aliphatic and alicyclic ketones, and approximately 70% for aromatic ketones and enones (eq 1).1-3 In these reactions the initial stereochemical (E)/(Z) ratio, of the 1,3-butadienyl group of the Grignard reagent was found to be retained in the reaction products.

Butadienylmagnesium chloride usually reacts at the carbonyl group of conjugated ketones, whereas in the presence of Copper(I) Iodide (addition of 50 mol % CuI forms the butadienylmagnesium CuI complex), 1,4-addition is observed (eq 2).

Grignard analogs of higher 1,3-dienes (penta-, hepta-, octa-)1 or their silylated derivatives (e.g. (E,E)-1 bromo-1-(trimethylsilyl)penta-1,3-diene)5 react with carbonyl compounds in a similar manner (eq 3).

For the introduction of the butadienyl moiety, Grignard reagents are preferred to the lithium derivatives due to the lower basicity of the former. The silylated pentadienyl Grignard reagent in eq 3 was superior to both the precursor lithium reagent and pentadienyllithium itself.5

Coupling with Alkyl Halides.

The coupling of 1,3-butadienyl-1-magnesium chloride with alkyl bromides or iodides is catalyzed by CuI and proceeds under mild conditions (eq 4).3 The stereochemistry of the dienyl moiety is retained in the reaction product. The coupling reaction with 5-bromo-2-methyl-1-penten-3-yne was accompanied by allene formation (eq 5).6

The configuration of the introduced butadienyl group corresponds to the configuration of the starting chlorobutadiene (for purification and isomerization of (Z)- and (E)-1-chlorobuta-1,3-dienes, see Onishchenko7). A mixture of (Z)- and (E)-isomers of the butadienyl derivatives obtained after reaction of butadienylmagnesium chloride with ketones and aldehydes could be transformed by the action of alkyllithium reagents, Dimethylphenylsilyllithium, Trimethylstannyllithium, or Lithium Diethylamide, into the pure (E)-diene with simultaneous lengthening of the chain (eq 6).2

4-Substituted-(Z,Z)-butadienyl cuprates can be prepared by addition of cuprates to alkynes. These form 1,4-disubstituted (Z,Z)-butadienes with typical electrophiles (alkyl halides, enones, CO2) (eq 7).8

Related Reagents.

1,3-Butadienyl-2-lithium; 1,3-Butadienyl-1-lithium; 1,3-Butadienyl-2-magnesium Chloride.

1. Solomon, P. W. U.S. Patent 1978, 4 087 468 (CA 1978, 89, 108 113r).
2. Ishii, T.; Kawamura, N.; Matsubara, S.; Utimoto, K.; Kozima, S.; Hitomi, T. JOC 1987, 52, 4416.
3. Kozima, S.; Ishii, T.; Tsuboi, T.; Kawanisi, M.; Mizuno, M.; Hitomi, T. Chem. Express 1987, 2, 301.
4. Watson, S. C.; Eastham, J. F. JOM 1967, 9, 165.
5. Wrobel, J. E.; Ganem, B. JOC 1983, 48, 3761.
6. Vorskanyan, S. A.; Fobanyan, Zh. A.; Badanyan, Sh. H. Arm. Khim. Zh. 1987, 40, 181 (CA 1988, 109, 22 675v).
7. Onishchenko, A. S.; Aronova, N. I. Proc. Acad. Sci. USSR, Chem. Sect., 1960, 132, 471.
8. Furber, M.; Taylor, R. J. K.; Burford, S. C. TL 1985, 26, 3285.

Viesturs Lūsis

Latvian Institute of Organic Synthesis, Riga, Latvia

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