1,3-dihaloalkane cyclopropane

Attempts to exploit the reaction of the dianion with alkyl halides to produce a c/.v-dialkyl complex by using 1,2- or 1,3-dihaloalkanes did not indeed give this result. The reaction of Ru(Por) " with 1,2-dibromoethane was sucessful, but the resulting metallacyclopropane product is better formulated as a /r-complex of ethene, and will be discussed below in the section on alkenc and alkyne complexes. The corresponding reaction of the diiinion with 1,3-dichloropropane gave no evidence for a metallacyclobutane. but instead free cyclopropane was detected by GC analysis and the porphyrin product was Ru(TTP)(THF)2. ... 

The predictable inversion of configuration that accompanies 8 2 substitution reactions can be used to convert stereoselectively labeled vicinal dihaloalkanes into stereoselectively labeled cyclopropanes. The dihaloalkanes can, themselves, be prepared by halogenation of stereoselectively labeled alkenes. Two examples are shown in Figure 8 and Figure 9 . 

Typically, attempts to synthesize 1,2-di-Grignard reagents from 1,2-dihaloalkanes fail, because metal halide elimination after insertion of the first magnesium atom is faster than formation of a second magnesium-carbon bond. The only l,2-di(halomagnesio)alkane [16] synthesized in the classic fashion is a l,2-di(bromomagnesio)cyclopropane 22 [Eq. 

C-C double bonds are elTiciently cyclopropanated electrochemically in a one-compartment cell fitted with a sacrificial zinc anode which allowed the formation of organozinc species from geminal dihaloalkanes. Electrolysis of dibromomethane in dichloromethane/dimethyl-formamide as solvent mixture is recommended as the standard condition for electrolysis. The best chemical yields were obtained with allylic alcohols and unfunctionalized alkenes. For example electrolysis of allyl alcohol 23 gave cyclopropane 24 in 70% yield. 

Further improvement of the Simmons-Smith cyclopropanation reaction is the use of trialkyl-aluminum to generate the cyclopropanating intermediate by reaction with dihaloalkanes. The reaction can be carried out under mild conditions and in nonpolar solvents and is stereospecific with respect to alkene substituents. This reaction is shown mechanistically for the generalized formation of 27, Specific examples are the formation of cw-1 -methyl-2-pentylcyclo-propane (28) from (Z)-oct-2-ene, and the formation of decylcyclopropane(93%), bicyclo[6.1.0] nonane (75%) and 1-phenyl-l-(trimethylsiloxy)cyclopropane (86%). 

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