54410-69-4

Iron-catalyzed cross-coupling reaction of alkyl halides with alkyl Grignard reagents by the combined use of cyclopentadienyl ligand and 1,3-butadiene additive is described. The reaction smoothly proceeds at room temperature using unactivated alkyl bromides and fluorides via non-radical mechanism, which is in sharp contrast with hitherto known Fe-catalyzed cross-coupling reactions of alkyl halides.

Styrene and a range of aryl-substituted styrene derivatives are shown to undergo efficient carbolithiation-trapping reactions in diethyl ether at -78 to -25 °C. The reactivities of different types of organolithium reagents were found to be: tertiary, secondary > primary; ? alkenyl, methyl, phenyl. Electron donating groups (e.g. methoxy and dialkylamino) at the ortho- or para- positions of the benzene ring deactivate the double bond towards organolithium addition, but their reactions with butyllithium can be facilitated by using TMEDA as co-solvent. 2-Benzyloxystyrene and 2-allyloxystyrene undergo efficient carbolithiation at -78 °C, but at room temperature alkyl transfer occurs, generating the corresponding alkylated phenol. 2-Vinylnaphthalene also undergoes carbolithiation-carboxylation in reasonable yield.

Radicals produced via the indirect reduction of alkyl halides by aromatic radical anions are likely to couple fast with the mediator. In the presence of activated olefins or good hydrogen atom donors the fate of the alkyl radicals might be changed. In this study rate constants for the coupling reaction (2) between primary, secondary and tertiary alkyl radicals and some aromatic radical anions were measured via the competition with addition of the radical to styrene or ethyl cinnamate, or via the competition with hydrogen atom transfer from thiophenol or 2-methyl-2-propanethiol to the alkyl radical. It is shown that for all the alkyl radicals and aromatic radical anions investigated so far the rate constant for coupling is close to 1 × 109 M-1 s-1. Acta Chemica Scandinavica 1998.

In diethyl ether at -78 to -25°C, styrene undergoes efficient addition reactions with a range of alkyllithium reagents, and the intermediate benzyllithiums can be trapped (e.g. with carbon dioxide and chlorotrimethylsilane); two aryl-substituted styrenes are shown to react in a similar manner.

Catalytic cyclometallation of styrene, m-methylstyrene, p-tert-butylstyrene, and 1-hexene with di n-alkylmagnesium compounds (n-R2Mg, where R=C3H7, C4H9, C6H13) in the presence of Cp2Zr2Cl2 has been given high yields of 2,4-disubstituted magnesiocyclopentanes.The probable mode of formation of magnesiocyclopentanes, involving zirconocyclopentanes formed from Cp2ZrCl2, n-R2Mg, and the appropiate olefins as reactive intermediates in the cyclometallation, is discussed. Keywords: catalytic synthesis, substituted styrenes, alkenes, magnesium alkyls.

The reaction of Cp2Zr(CH2CH2R1)2 with a monosubstituted terminal alkene (H2C=CHR2) can produce, in a highly regio- and diastereoselective manner, zirconacyclopentane derivatives; the trans-3,4-disubstituted derivatives may be formed to the extents of >98percent in cases where both R1 and R2 are alkyl, while the trans-2-aryl-4-alkyl derivatives may be formed to the extents of >98percent in the coupling between a monoalkyl-substituted olefin and styrene or its derivative.