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14.11 Alkane Synthesis Using Organocopper Reagents

14.11 Alkane Synthesis Using Organocopper Reagents. 2R Li + Cu X. R 2 Cu Li + Li X. [customary solvents are diethyl ether and tetrahydrofuran (THF)]. Lithium Dialkylcuprates. Lithium dialkylcuprates are useful synthetic reagents.

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14.11 Alkane Synthesis Using Organocopper Reagents

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  1. 14.11Alkane Synthesis Using Organocopper Reagents

  2. 2RLi + CuX R2CuLi + LiX [customary solvents are diethyl ether and tetrahydrofuran (THF)] Lithium Dialkylcuprates Lithium dialkylcuprates are useful synthetic reagents. They are prepared from alkyllithiums and a copper(I) halide.

  3. R Li R Cu Cu I then a second molecule of the alkyllithium reacts with the alkylcopper species formed in the first step R Li+ R Li R Cu – R Cu How? the alkyllithium first reacts with the copper(I) halide Li+ I–

  4. + + + R'X LiX R R' RCu R2CuLi Lithium diorganocuprates are used toform C—C bonds + + + R'X LiX Ar R' ArCu Ar2CuLi

  5. Example: Lithium dimethylcuprate + (CH3)2CuLi CH3(CH2)8CH2I primary alkyl halides work best (secondary and tertiary alkyl halides undergo elimination) diethyl ether CH3(CH2)8CH2CH3 (90%)

  6. Example: Lithium diphenylcuprate + (C6H5)2CuLi CH3(CH2)6CH2I diethyl ether CH3(CH2)6CH2C6H5 (99%)

  7. CH2CH2CH2CH3 Vinylic halides can be used + Br (CH3CH2CH2CH2)2CuLi diethyl ether (80%)

  8. Aryl halides can be used + I (CH3CH2CH2CH2)2CuLi diethyl ether CH2CH2CH2CH3 (75%)

  9. 14.12An Organozinc Reagent forCyclopropane Synthesis

  10. Iodomethylzinc iodide formed by reaction of diiodomethane withzinc that has been coated with copper(called zinc-copper couple) reacts with alkenes to form cyclopropanes reaction with alkenes is called theSimmons-Smith reaction Cu CH2I2 + Zn ICH2ZnI

  11. Example CH2CH3 CH2CH3 CH2I2, Zn/Cu H2C C CH3 diethyl ether CH3 (79%)

  12. CH3CH2 CH2CH3 C C H H CH3CH2 CH2CH3 H H Stereospecific syn-addition CH2I2, Zn/Cu diethyl ether

  13. C C CH2I2, Zn/Cu diethyl ether CH3CH2 H H CH2CH3 Stereospecific syn-addition CH3CH2 H H CH2CH3

  14. 14.13Carbenes and Carbenoids

  15. •• C Br Br dibromocarbene Carbene name to give to species that contains adivalent carbon (carbon with two bondsand six electrons) Carbenes are very reactive; normally cannot be isolated and stored. Are intermediates in certain reactions.

  16. – •• OC(CH3)3 C • • •• Br •• – + OC(CH3)3 H Br C • • •• Br Generation of Dibromocarbene Br + Br H Br

  17. Br – Br C • • Br Generation of Dibromocarbene •• C – + Br Br Br

  18. Carbenes react with alkenesto give cyclopropanes CBr2 is an intermediate stereospecific syn addition Br KOC(CH3)3 + CHBr3 (CH3)3COH Br (75%)

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