Jr. Al Dulayymi et al., Hydrodehalogenation of 1,1-dibromocyclopropanes by Grignard reagents promoted by titanium compounds, J CHEM S P2, (7), 2000, pp. 1603-1617
Citations number
114
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2
1,1-Dibromocyclopropanes are converted into the corresponding monobromocycl
opropanes (as mixtures of stereoisomers where appropriate) by reaction with
1.0-1.3 mol equiv. of ethylmagnesium bromide and 2-10 mol% titanium isopro
poxide for < 1 h in ether at ambient temperature; in most cases examined, t
he yields were ca. 95%. With an excess of the Grignard reagent, the product
is the non-halogenated cyclopropane (> 90%). With ethylmagnesium bromide,
the reaction occurs very slowly in the absence of catalyst; with methylmagn
esium bromide, the reaction does occur in the absence of catalyst, but is o
nly slightly promoted in the presence of titanium isopropoxide. Reactions w
ith a number of other Grignard reagents are also discussed. In the case of
phenethylmagnesium bromide, the major product containing the phenethyl-grou
p is ethylbenzene, together with small amounts of styrene and ethyl 4-pheny
l-2-butyl ether, a product of trapping of the solvent, ether. In other case
s, relatively large amounts of a diether, formally derived by hydrogen abst
raction adjacent to the ether oxygen followed by dimerisation, are isolated
. No products were identified incorporating the cyclopropane and either the
Grignard alkyl group or the solvent. Labelling studies indicate that the h
ydrogen introduced into the cyclopropane is not derived from either the alp
ha- or beta-positions of the Grignard reagent. When the reduction is carrie
d out with phenethylmagnesium bromide in d(8)-tetrahydrofuran both monobrom
ides contain deuterium.