[23179-80-4] · C3H5BrMg · Cyclopropylmagnesium Bromide · (MW 145.30)
Solubility: sol ethereal solvents.
Form Supplied in: solution in ether or THF.
Analysis of Reagent Purity: it is highly recommended to analyze every batch of cyclopropylmagnesium bromide by using one of the standard titration methods.5
Preparative Methods: cyclopropylmagnesium bromide is best prepared by treating magnesium turnings with commercially available cyclopropyl bromide in THF.6a Yields usually range from 23 to 43%. Reaction in ether gives even lower yields,6 mainly due to the extensive disproportionation of cyclopropyl radicals on the magnesium surface.6a
Handling, Storage, and Precautions: Grignard reagent solutions are highly flammable and moisture sensitive.
Cyclopropylmagnesium bromide reacts smoothly with aldehydes and ketones to give secondary2 and tertiary7 alcohols, respectively (eqs 1 and 2). Controlled reaction with N,N-Dimethylformamide gives rise to the formation of cyclopropanecarbaldehyde in good yield (eq 3).8
Direct oxidation of cyclopropylmagnesium bromide with molecular oxygen affords the ellusive cyclopropanol, albeit in low yield (eq 4).2 Conversion to cyclopropylmercury(II) bromide followed by reaction with aqueous KI-I2 leads to cyclopropyl iodide (eq 5).2
Cyclopropylmagnesium bromide couples, in the presence of a nickel catalyst, with aryl and vinyl bromides to give the corresponding aryl- and vinylcyclopropanes (eqs 6 and 7).9
Other interesting synthetic applications of cyclopropylmagnesium bromide include formation of cyclopropyl ketones from acyl halides (via dicyclopropylcadmium),10 conversion of optically pure p-tolylsulfinate to cyclopropyl tolyl sulfoxide with virtually complete inversion of configuration at sulfur,11 and coupling with methyl a-chloro-N-benzyloxycarbonylglycinate.12
Cyclopropylalkyl alcohols, prepared from cyclopropylmagnesium bromide and appropriate carbonyl compounds, readily rearrange to homoallylic bromides3,13 upon treatment with Hydrobromic Acid. The entire conversion can be conducted without isolation of the intermediate carbinol (eq 8).14
Cyclopropylmagnesium bromide reacts with aromatic dithioacetals in boiling benzene or toluene, in the presence of a nickel catalyst, to give aryl-substituted dienes in good yields (eq 9).4
Harry M. Walborsky & Marek Topolski
Florida State University, Tallahassee, FL, USA