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REACTIONS WITH EPOXIDES

REACTIONS WITH EPOXIDES. PRIMARY ALCOHOLS. Reaction with Oxirane. ether. H 3 O +. +. R. Notice that :. the carbon chain has added two carbons. the product is a terminal alcohol. Crude outline of a mechanism. alkoxide ion. +. Li. Workup step. usually dilute HCl. O. H. R. C.

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REACTIONS WITH EPOXIDES

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  1. REACTIONS WITH EPOXIDES PRIMARY ALCOHOLS

  2. Reaction with Oxirane ether H3O+ + R Notice that : • the carbon chain has added two carbons • the product is a terminal alcohol

  3. Crude outline of a mechanism alkoxide ion + Li Workup step usually dilute HCl

  4. O H R C H C H N u C H C H 2 2 REACTION IS AT THE LEAST-SUBSTITUTED CARBON O N u : + R Why?

  5. REACTIONS WITH EPOXIDES Notice which carbon was attacked by the nucleophile. Grignard reagents could have been used instead of alkyllithiums.

  6. REACTION WITH OXETANES

  7. Oxetanes add a three Carbon Piece

  8. ORGANOMETALLICS FROM ALKYNES

  9. Acetylenic Grignard Reagents Acetylenic Grignard Reagents cannot be made directly. They must be made by exchange.

  10. Alkynylorganometallic Compounds React another organometallic compound with an alkyne (= exchange). basic cannot be prepared directly - you must use exchange acidic H preparation of methyllithium CH3-Br + 2 Li CH3-Li + LiBr ether + exchange +

  11. LITHIUM DIALKYL CUPRATES

  12. LITHIUM DIALKYLCUPRATES R2CuLi Made by treating an alkyllithium compound with copper (I) iodide.

  13. CH3 H3C Cu CH3 Li Li Cu CH3 STRUCTURE OF THE LITHIUM DIALKYLCOPPER COMPLEX This structure is an oversimplification. The actual complex is known to be a dimer. Although there is a great deal of debate, Li2Cu2(CH4)4 is thought to have a “cluster” structure similar to the one shown below. R CuLi R The mechanism by which it works is complicated. It probably involves single electron transfers to the substrate making radicals which combine. We will show the reactions and not attempt to draw any mechanism. NOTE: This is a structure of a crystal and may not be the structure of the reagent in solution.

  14. ALKYLATION WITH R2CuLi 0o C R-X + R2CuLi R-R + R-Cu + LiX ether X = Cl, Br, I EXAMPLES (CH3)2CuLi + CH3(CH2)4-I CH3-(CH2)4-CH3 + Corey-House Reaction

  15. COMPARE R2CuLi TO THE WURTZ REACTION The Wurtz reaction gives only symmetric coupling R-R C5 - C5 Must be aliphatic. Lithium Dialkylcuprates can give asymmetric coupling R-R’ C5 - C2 Can also be an alkene or an aromatic compound.

  16. (CH3CH2)2CuLi MORE LITHIUM DIALKYLCUPRATE COUPLING + KOH CHBr3

  17. R2CuLi (CUPRATES) WITH ACID CHLORIDES Cuprates can also couple with acid chlorides. + ACID CHLORIDE KETONE

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