J.W.F.L. Seetz

A direct synthesis of 1,3-bis(bromomagnesio)propane

Abstract Careful addition of 1,3-dibromopropane to magnesium in Et 2 O yields 1,3-bis(bromomagnesio)propane which is purified via “magnesacyclobutane” . Reactions of with H 2 O, CO 2 , HgBr 2 and Me 3 SnCl are reported. MgBr 2 catalyses the decomposition of to allylmagnesium bromide .

A general synthesis of metallacyclobutanes

Abstract Metallacycloalkanes containing four to six carbon atoms are easily synthesized from α,ω-dimetal-organic compounds and the appropriate metal dihalide. Metallacyclobutanes were not accessible in this way however, as the corresponding organometallic reagents were not easily available. However, our recent synthesis of di-Grignard reagents from 1,3-dibromopropanes allowed the development of a general synthesis of the title compounds. In addition to the synthesis in high yields of the (already known) germana- and titana-cyclobutanes, the method has also proved useful in the preparation of stanna-, hafna-, zircona- and vanada-cyclo butanes. The newly prepared compounds have been characterized by their NMR spectra (plus the ESR spectrum for the paramagnetic vanadium compound) and the products of their reaction with elemental bromine. Their behaviour as organometallic compounds has been derived from their reactions with cyclohexanone. The scope and limitations of the synthesis appear to be mainly determined by the stability of the 1,3-di-Grignard compounds, which is strongly dependent on the substitution pattern.

The synthesis and structure of zinccacyclopentane, zincacyclohexane and zincacycloheptane

Abstract The first bifunctional zinc compounds of 1,4-dibromobutane, 1,5-dibomopentane and 1,6-dibromohexane have been prepared by use of Rieke zinc; extraction of the salt mixture obtained after evaporation of the solvent THF with a diethyl ether/dioxane mixture yielded the title compounds. The new compounds are characterized by their 1 H and 13 C NMR spectra. Association measurements on THF solutions of the zincacycloalkanes at concentrations up to about 0.04 M at 28.50°C indicated a dimeric structure. Comparisons with the magnesium analogues are made.

A convenient synthesis of germacyclobutanes

Abstract The reaction of the di-Grignard reagents BrMgCH 2 CR 2 CH 2 MgBr ( 2a : R = H; 2b : R = Me) with dichlorodimethylgermane gave 1,1-dimethylgermacyclobutane ( 1a ) and its 3,3-dimethyl derivative 1b , respectively, in more than 95% yield.

1,1-Dicyclopentadienyl-3,3-dimethylvanada(IV) cyclobutane

Abstract The reaction of 1,3-bis(bromomagnesio)-2,2-dimethylpropane (1b) with dichlorodicyclopentadienylvanadium(IV) (5) gave 1,1-dicyclopentadienyl-3,3-dimethylvanada(IV)cyclobutane (4) in 30% yield, contaminated with dicyclopentadienylneopentylvanadium(III) (12). Attempts to purify 4 were only partially successful due to its limited stability (t 1 2 = 4 h at 25°C in cyclopentane). Identification of 4 is therefore based on its having sufficient thermal stability for isolation, on its reaction with bromine to give 1,3-dibromo-2,2-dimethylpropane (2b), and especially on its ESR and 1H NMR spectra. The reaction of 4 with cyclohexanone (15) gave 17 and 18 as the main products; 17 is the aldol dimer of 15, while 18 may be derived from either 4 or 12. Because methylenecyclohexane (16) is not one of the reaction products, it is concluded that 4 does not have a pronounced tendency to fragment to give a metallacarbene (20).

1,2-dimagnesium derivatives of cyclopropane

Abstract cis-1,2-Dibromomagnesiocyclopropane (cis- 4 ) was isolated from the reaction of both trans- and cis-1,2-dibromocyclopropane ( 1 ) with magnesium. The corresponding dialkylmagnesium species ( 7 ), an oligomer of 2-magnesabicyclobutane, was obtained from cis- 4 by precipitation in THF; it forms a soluble complex 8 with HgBr 2 .

The synthesis of cis- and trans-1,2-dibromocyclopropane

Abstract A preparative route to cis- and trans-1,2-dibromocyclopropane ( 1 ) was developed via the Hunsdiecker reaction of silver cyclopropane-1,2-dicarboxylate ( 2 ). Cis- and trans- 2 gave the same ratio of cis- and trans- 1 (1:3.2). The mechanism of this reaction is briefly discussed.