Cyclopropylmagnesium compounds

Scheme 4.49 Stereoselective preparation of functionalized cyclopropylmagnesium compounds.

The reaction of metals with alkyl halide to form alkylmetal compounds is typical for lithium and magnesium. This so-called direct synthesis was applied to the preparation of both cyclopropyllithium" and derivatives and cyclopropylmagnesium halides under the standard preparative conditions of Grignard reagents without ring cleavage (equation 1). 

Many cyclopropyl halides, mainly bromides, but also some chlorides, have been converted to alkylcyclopropanes by replacement of the halide. The yields reported are usually well above 50%. Several types of reactions have been utilized to achieve such substitution. When simple halocyclopropanes are used, the halides are converted to the corresponding cyclopropyllithium compounds or cyclopropylmagnesium halides, which undergo alkylation when treated with electrophiles such as alkyl halides, dimethyl sulfate, and tropenylium tetrafluoroborate. Following this strategy 3-bromo-l,l,2,2-tetramethylcyclopropane, bromocyclopropane and (la,2/I,3a)-1-bromo-2,3-dimethyl-l-phenylcyclopropane were transformed to 1,1,2,2,3-penta-... 

Tricyclopropylbismuth and dicyclopropylbismuth chloride are obtained by reaction of cyclopropylmagnesium bromide with Bids according to the required stoichiometry. These organobismuth compounds are useful for iV-cyclopropylation of lactams such as phenanthridinone. ... 

Cyclopropylmagnesium carbenoids (75) generated by treatment of a-chlorosulfoxide (74) with /-PrMgCl have been shown to insert into the C-C bond of /3-aryl carbonyl compounds (Scheme 10). This insertion results from the reaction between (75) (g) and the enolate of the carbonyl compound (76) and thus corresponds to a valuable one-carbon homologation reaction or a ring-expansion reaction, as illustrated by the isolation of (77), from cyclic starting material. The insertion process proceeds in a... 

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