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14.11 Alkane Synthesis Using Organocopper Reagents

14.11 Alkane Synthesis Using Organocopper Reagents. Dr. Wolf's CHM 201 & 202. 14-53. Lithium Dialkylcuprates. Lithium dialkylcuprates are useful synthetic reagents. They are prepared from alkyllithiums and a copper(I) halide. 2RLi + Cu X. R 2 Cu Li + Li X.

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14.11 Alkane Synthesis Using Organocopper Reagents

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  1. 14.11Alkane Synthesis Using Organocopper Reagents Dr. Wolf's CHM 201 & 202 14-53

  2. Lithium Dialkylcuprates Lithium dialkylcuprates are useful synthetic reagents. They are prepared from alkyllithiums and a copper(I) halide. 2RLi + CuX R2CuLi + LiX [customary solvents are diethyl ether and tetrahydrofuran (THF)] Dr. Wolf's CHM 201 & 202 14-54

  3. R Li R Cu Cu I How? the alkyllithium first reacts with the copper(I) halide Li+ I– Dr. Wolf's CHM 201 & 202 14-55

  4. R Li R Cu Cu I R R Li R Cu R Cu How? the alkyllithium first reacts with the copper(I) halide Li+ I– then a second molecule of the alkyllithium reacts with the alkylcopper species formed in the first step Li+ – Dr. Wolf's CHM 201 & 202 14-56

  5. + + + R'X LiX R R' RCu R2CuLi Lithium diorganocuprates are used toform C—C bonds + + + R'X LiX Ar R' ArCu Ar2CuLi Dr. Wolf's CHM 201 & 202 14-57

  6. 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%) Dr. Wolf's CHM 201 & 202 14-58

  7. Example: Lithium diphenylcuprate + (C6H5)2CuLi CH3(CH2)6CH2I diethyl ether CH3(CH2)6CH2C6H5 (99%) Dr. Wolf's CHM 201 & 202 14-59

  8. CH2CH2CH2CH3 Vinylic halides can be used + Br (CH3CH2CH2CH2)2CuLi diethyl ether (80%) Dr. Wolf's CHM 201 & 202 14-60

  9. Aryl halides can be used + I (CH3CH2CH2CH2)2CuLi diethyl ether CH2CH2CH2CH3 (75%) Dr. Wolf's CHM 201 & 202 14-61

  10. 14.12An Organozinc Reagent forCyclopropane Synthesis Dr. Wolf's CHM 201 & 202 14-62

  11. 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 Dr. Wolf's CHM 201 & 202 14-63

  12. Example CH2CH3 CH2CH3 CH2I2, Zn/Cu H2C C CH3 diethyl ether CH3 via (79%) I CH2 ZnI Dr. Wolf's CHM 201 & 202 14-64

  13. CH3CH2 CH2CH3 C C H H Stereospecific syn-addition CH2I2, Zn/Cu diethyl ether CH3CH2 CH2CH3 H H Dr. Wolf's CHM 201 & 202 14-65

  14. C C Stereospecific syn-addition CH3CH2 H H CH2CH3 CH2I2, Zn/Cu diethyl ether CH3CH2 H H CH2CH3 Dr. Wolf's CHM 201 & 202 14-66

  15. 14.13Carbenes and Carbenoids Dr. Wolf's CHM 201 & 202 14-67

  16. •• C Br Br Dibromocarbene Carbene name to give to species that contains adivalent carbon (carbon with two bondsand six electrons) (same chemistry with dichlorocarbenes) Carbenes are very reactive; normally cannot be isolated and stored. Are intermediates in certain reactions. Dr. Wolf's CHM 201 & 202 14-68

  17. – •• OC(CH3)3 C • • •• Br – H Br C • • Br Generation of Dibromocarbene Br + Br H Br •• + OC(CH3)3 •• Dr. Wolf's CHM 201 & 202 14-69

  18. – Br Br – Br C • • Br Generation of Dibromocarbene •• C + Br Br Dr. Wolf's CHM 201 & 202 14-70

  19. Carbenes react with alkenesto give cyclopropanes CBr2 is an intermediate stereospecific syn addition Br KOC(CH3)3 + CHBr3 (CH3)3COH Br (75%) Dr. Wolf's CHM 201 & 202 14-71

  20. End of Chapter 14

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