- Hydrodehalogenation of 1,1-dibromocyclopropanes by Grignard reagents promoted by titanium compounds
-
1,1-Dibromocyclopropanes are converted into the corresponding monobromocyclopropanes (as mixtures of stereoisomers where appropriate) by reaction with 1.0-1.3 mol equiv. of ethylmagnesium bromide and 2-10 mol% titanium isopropoxide for 90%). With ethylmagnesium bromide, the reaction occurs very slowly in the absence of catalyst; with methylmagnesium bromide, the reaction does occur in the absence of catalyst, but is only slightly promoted in the presence of titanium isopropoxide. Reactions with a number of other Grignard reagents are also discussed. In the case of phenethylmagnesium bromide, the major product containing the phenethyl-group is ethylbenzene, together with small amounts of styrene and ethyl 4-phenyl-2-butyl ether, a product of trapping of the solvent, ether. In other cases, relatively large amounts of a diether, formally derived by hydrogen ion 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 hydrogen introduced into the cyclopropane is not derived from either the α- or β-positions of the Grignard reagent. When the reduction is carried out with phenethylmagnesium bromide in d8-tetrahydrofuran both monobromides contain deuterium.
- Dulayymi, Juma'a R. Al,Baird, Mark S.,Bolesov, Ivan G.,Nizovtsev, Alexey V.,Tverezovsky, Viacheslav V.
-
p. 1603 - 1618
(2007/10/03)
-
- Highly regioselective reaction of zirconocene-alkene complexes with aldehydes or ketones
-
Reactions of zirconocene-alkene complexes Cp2Zr(CH2=CHR)(PR'3) (R = H, Me, Et, SiR"3 or Ar) with aldehydes or ketones were investigated.Zirconocene-ethylene, -propylene or 1-butene complexes reacted with aldehydes or ketones at terminal carbons of alkenes to give the corresponding alcohols after hydrolysis with a high regioselectivity.A similar type of reaction product was also obtained by a reaction of zirconacyclopentanes with aldehydes.This reaction proceeded via β-β' carbon-carbon bond cleavage of zirconacyclopentanes.A reaction of zirconocene-vinylsilane complexes with ketones afforded 3-trimethylsilyl-1-oxa-2-zirconacyclopentanes with an excellent regioselectivity.Carbon-carbon bond formation occurred exclusively at the terminal carbon of vinylsilanes.Their corresponding γ-silylalcohols were obtained after hydrolysis.The products showed that vinylsilanes reacted with carbonyl compounds at the β-carbon to silyl group.It is in sharp contrast to the conventional reactions of vinylsilanes of which the α-carbon normally attacked electrophiles.The reactions of styrene and its derivatives with pentan-3-one on zirconium gave a mixture of two regioisomers.Substituents of alkenes tend to be in α-position to Zr in 1-oxa-2-zirconacyclopentanes.This orientation showed a different aspect of the formation of 1-oxa-2-zirconacyclopentanes from the alkene-alkene coupling reaction on zirconium.The regioselectivity of the reaction with carbonyl compounds decreased in this order; R = alkyl > silyl > aryl. Key words: Zirconium; Silicon; Metallocenes; Carbon-carbon bond formation; Aldehyde; Ketone
- Suzuki, Noriyuki,Rousset, Christophe J.,Aoyagi, Koichiro,Kotora, Martin,Takahashi, Tamotsu,et al.
-
p. 117 - 128
(2007/10/02)
-
- REACTION OF ALKYLMAGNESIUM HALIDES WITH CARBOXYLIC ESTERS IN THE PRESENCE OF TETRAISOPROPOXYTITANIUM
-
The reaction of carboxylic esters with a threefold molar excess of ethylmagnesium bromide in the presence of an equimolar amount of tetraisopropoxytitanium leads to the formation of the corresponding 1-substituted 1-cyclopropanols.Propyl-, butyl-,and 2-phenylethylmagnesium bromides enter into a similar reaction, leading to 1,2-disubstituted 1-cyclopropanols.
- Kulinkovich, O.G.,Sviridov, S.V.,Vasilevskii, D.A.,Savchenko, A.I.,Pritytskaya, T.S.
-
p. 250 - 253
(2007/10/02)
-
- Substitution Reactions of Secondary Halides and Epoxides with Higher Order, Mixed Organocuprates, R2Cu(CN)Li2: Synthetic, Stereochemical, and Mechanistic Aspects
-
Higher order cuprates, represented by the general formula R2Cu(CN)Li2, are readily prepared from copper cyanide and 2 equiv of an organolithium.These novel reagents react readily and efficiently with secondary unactivated iodides and bromides affording products of substitution.Likewise, mono-, di-, and trisubstituted epoxides undergo ring opening leading to the corresponding alcohols in excellent yields.The effects of solvent, temperature, gegenion, and variations in ligands are discussed.Replacement of the second equivalent of RLi by CH3Li strongly encouragestransfer of R over CH3 in R(CH3)Cu(CN)Li2 with halides.Use of PhLi as RRLi in place of one RTLi (i.e.RT(Ph)Cu(CN)Li2) is suggested for oxirane cleavage.The stereochemical implications associated with both couplings are also addressed.
- Lipshutz, Bruce H.,Wilhelm, Robert S.,Kozlowski, Joseph A.,Parker, David
-
p. 3928 - 3938
(2007/10/02)
-
- Stereochemistry of Aliphatic Carbocations, 13. Protonated Cyclopropanes as Intermediates in 1,2-Alkyl Shifts
-
The nitrous acid deamination of 2-ethyl-1-methylbutylamine (10), 1,2-diethylbutylamine (35), and 2-ethyl-1-methylpentylamine (43) has been studied with respect to 1,2-alkyl shifts.Optically active and deuterated amines were employed whenever possible.The structure, configuration, and deuterium distribution of various products (e. g. 16 from 10, 40 and 48 from 35, 56 from 43) are most reasonably explained in terms of alkyl-bridged intermediates (corner-protonated cyclopropanes) which isomerize via proton shifts from corner to corner.The alternative interconversion of open ions via 1,3-H shifts is incompatible with our experimental results.
- Kirmse, Wolfgang,Loosen, Karin,Prolingheuer, Ernst-Christoph
-
p. 129 - 141
(2007/10/02)
-