[26220-97-3] · C3H9FeLi · Trimethylironlithium · (MW 107.91)
Alternate Name: lithium trimethylferrate.
Preparative Method: prepared in situ by reaction of FeI2 and MeLi in ether.
Handling, Storage, and Precautions: decomposes in solution at 0 °C after several hours.
Alkylation of alkyl halides using organocopper reagents has been widely studied.1 Other organometallic reagents have also been studied for their efficacy in carbon-carbon bond formation, including trimethylironlithium.2
The reagent appears to work most effectively with vinyl, phenyl, and primary alkyl halides. However, it is generally ineffective with secondary and tertiary alkyl halides, under the conditions examined (Table 1). The reaction between trimethylironlithium and organohalides is considerably faster than similar reagents prepared from manganese or cobalt. The reaction of tri-n-butylironlithium with organohalides failed.
In general, trialkylironlithium appears to be inferior to organocuprates in effecting carbon-carbon bond formation. However, it has been found to be superior to organocuprates and other methylating reagents in special cases.3 For instance, the methylation of allyl bromide (1) gave the corresponding alkene (2) in excellent yield, without an allylic transposition4 that was found to occur with lithium dimethylcuprate (eq 1).
The methylation of cyclohexenone (3) with trimethylironlithium gave the conjugate addition product, 3-methylcyclohexanone (4), in 26% yield, and cyclohexenol (5), in 28% yield (eq 2). Greater regioselectivity to produce cyclohexanone (4) is achieved with organocuprates and organomanganese reagents.
The reaction of trimethylironlithium with epoxyvinyl sulfone (6) gave predominantly ketone (7) and reduction product (8) rather than the anticipated 1,2- and 1,4-addition products (eq 3).6
Mark W. Zettler
The Dow Chemical Company, Midland, MI, USA