Preparation of Organolithium Reagents

Summary

• Organolithiums are formed by the reaction of alkyl halides with lithium metal.
• Typical solvents are normally anhydrous diethyl ether but pentane or hexane can also be used.
• The alkyl group can be primary, secondary or tertiary.
• Halide reactivity : I > Br > Cl
• R can be alkyl, vinyl or aryl
• Other Group I metals (Na, K) can be used instead of Li.

• What is the oxidation state change for the C in the reaction methyl iodide to methyl lithium ? 
• What is the oxidation state change for the Li in the reaction methyl iodide to methyl lithium ? 
• What is the oxidation state change for the I in the reaction methyl iodide to methyl lithium ? 

Preparation of Organomagnesium Reagents

Summary

• Organomagnesiums are formed by the reaction of alkyl halides with magnesium metal.
• Typical solvents are normally anhydrous diethyl ether or tetrahydrofuran.
• The alkyl group can be primary, secondary or tertiary.
• Halide reactivity : I > Br > Cl
• R can be alkyl, vinyl or aryl.

• What is the oxidation state change for the C in the reaction methyl iodide to methyl magnesium iodide ? 
• What is the oxidation state change for the Mg in the reaction methyl iodide to methyl magnesium iodide ? 
• What is the oxidation state change for the I in the reaction methyl iodide to methyl magnesium iodide ? 

Preparation of Organocopper Reagents

• The most useful organocopper reagents are lithium dialkylcuprates, R₂CuLi.
• Lithium dialkylcuprates are formed by the reaction of 2 equivalents of an organolithium with a copper (I) halide.
• Typical solvents are normally anhydrous diethyl ether or tetrahydrofuran.
• The alkyl group is usually primary. Secondary and tertiary are prone to decomposition.
• Halide reactivity : I > Br > Cl
• R can be alkyl, vinyl or aryl.

Summary

• Organozinc reagents, RZnX, are prepared in a fashion analogous to that of organomagnesium reagents RMgX.
• They are much less reactive than either RLi or RMgX to aldehydes and ketones.
• The most common application of organozinc reagents is in the Simmons-Smith reaction

Preparation of Acetylenic Reagents

Summary

• In Ch9 we saw that terminal acetylenes can be deprotonated using sodium amide, NaNH₂ (review )

• Alternatively acetylenic Grignard reagents, RCºCMgX, can also be prepared.
• Rather than starting from the acetylenic halides, they are prepared by an acid-base reaction of the terminal acetylene with a second Grignard reagent.
• Acetylenic Grignards react in a similar fashion to other Grignard reagents.