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Epoxidation of Alkenes

Epoxidation of Alkenes. CHCH 3. H 2 C. CH 2. H 2 C. O. O. Epoxides. are examples of heterocyclic compounds three-membered rings that contain oxygen ethylene oxide propylene oxide. H 3 C. CHCH 3. CHCH 3. H 2 C. C. H 3 C. O. O. Epoxide Nomenclature.

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Epoxidation of Alkenes

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  1. Epoxidation of Alkenes

  2. CHCH3 H2C CH2 H2C O O Epoxides • are examples of heterocyclic compounds • three-membered rings that contain oxygen • ethylene oxide propylene oxide

  3. H3C CHCH3 CHCH3 H2C C H3C O O Epoxide Nomenclature • Substitutive nomenclature: named as epoxy-substituted alkanes. • “epoxy” precedes name of alkane • 1,2-epoxypropane 2-methyl-2,3-epoxybutane 1 4 2 3

  4. O H H Give the IUPAC name, including stereochemistry, for disparlure. • cis-2-Methyl-7,8-epoxyoctadecane

  5. O C RCOOH C O + RCOH C C O Epoxidation of Alkenes + peroxy acid

  6. O + CH3COOH O + CH3COH O (52%) Example

  7. O C RCOOH C O + RCOH C C O Stereochemistry of Epoxidation + syn addition

  8. H H O H H Give the structure of the alkene,including stereochemistry, that you wouldchoose as the starting material in a preparationof synthetic disparlure. Is disparlure chiral? Disparlure is chiral peroxy acid

  9. Epoxidation of cis-2-Butene • syn addition to cis-2-butene gives meso diastereomer R S RCO3H S R meso

  10. Question • The epoxidation of trans-2-butene produces: • A single enantiomer • A product with one asymmetric carbon atom • An optically inactive meso product • A racemic mixture • 4 different stereoisomers each with 2 chiral carbon atoms

  11. Relative Rates of Epoxidation • ethylene H2C=CH2 1 • propene CH3CH=CH2 22 • 2-methylpropene (CH3)2C=CH2 484 • 2-methyl-2-butene (CH3)2C=CHCH3 6526 • More highly substituted double bonds react faster.Alkyl groups on the double bond make itmore “electron rich.”

  12. Question • Which reagent reacts with an alkene to produce an epoxide? • A) B) • C) D)

  13. Ozonolysis of Alkenes • Ozonolysis has both synthetic and analytical applications. • synthesis of aldehydes and ketones • identification of substituents on the double bond of an alkene

  14. O C C C C O O Ozonolysis of Alkenes • First step is the reaction of the alkene with ozone.The product is an ozonide. + O3

  15. O C C C C O O O C Ozonolysis of Alkenes • Second step is hydrolysis of the ozonide. Two aldehydes, two ketones, or an aldehyde and a ketone are formed. + O3 H2O, Zn + O C

  16. O C C C C O O O O C C Ozonolysis of Alkenes • As an alternative to hydrolysis, the ozonide canbe treated with dimethyl sulfide. + O3 (CH3)2S +

  17. CH2CH3 CH3 C C H CH2CH3 CH2CH3 CH3 + O O C C H CH2CH3 (38%) (57%) Example 1. O3 2. H2O, Zn

  18. Question What are the products of the following reaction? A, C A, D A, E B, C B, E

  19. Question • The ozonolysis of 2,4-dimethyl-2-pentene will produce: • A) B) • C) D)

  20. Introduction to OrganicChemical SynthesisPlanning Reaction Steps & Linking ReactionsMUST have a command of many reactions

  21. Question a. A = 1; B = 4; C = 1; D = 1; E = 2, 6 b. A = 1; B = 8; C = 1; D = 6; E = 2, 6 c. A = 5; B = 4; C = 6; D = 1; E = 2, 6 d. A = 5; B = 8; C = 1; D = 6; E = 2, 6 e. A = 5; B = 4; C = 1; D = 1; E = 2, 6

  22. Example: transvicinal diols

  23. Question Which reagent(s) will produce the product in the following reaction? A. KMnO4, NaOH, coldB. 1) OsO4, pyridine 2) NaHSO3, H2OC. 1) MCPBA 2) H3O+ D. OsO4 (catalytic), NMO E. all of the above

  24. Retrosynthesis

  25. OH Prepare cyclohexane from cyclohexanol • devise a synthetic plan • reason backward from the target molecule • always use reactions that you are sure will work

  26. Prepare cyclohexane from cyclohexanol • ask yourself the key question • "Starting with anything, how can I make cyclohexane in a single step by a reaction I am sure will work?" H2 Pt

  27. Prepare cyclohexane from cyclohexanol • The only reaction covered so far for preparing alkanes is catalytic hydrogenation of alkenes. • This leads to a new question. "Starting with anything, how can I prepare cyclohexene in a single step by a reaction I am sure will work?" H2 Pt

  28. H2SO4 OH heat Prepare cyclohexane from cyclohexanol • Alkenes can be prepared by dehydration of alcohols. • The synthesis is complete. H2 Pt

  29. Question List the correct order of reagents to accomplish the following synthesis. H, B H, C H, D I, B I, D

  30. Question • Which one of the following outlines the best synthesis of trans-2-chlorocyclohexanol? • A) Heat a mixture of cyclohexanol and Cl2 to 400oC. • B) 1. Treat cyclohexene with HCl; • 2. Treat product of reaction 1 with peroxyacetic acid. • C) 1. Hydrogenation of cyclohexene in the presence of Pt; • 2. Treat product of reaction 1 with Cl2 in H2O. • D) 1. Treat bromocyclohexane with KOC(CH3)3 in DMSO; • 2. Treat product of reaction 1 with Cl2 in water.

  31. Question • Which one of the following is not stereospecific? • A) reaction of cis-2-butene with peroxyacetic acid • B) hydroboration-oxidation of 1- methylcyclopentene • C) addition of Br2 to trans-2-pentene • D) addition of HBr to cis-2-butene in the presence of peroxides

  32. Question • Which combination of reagents is the best choice for carrying out the conversion shown? • A) 50% water - 50% sulfuric acid • B) 1. H2SO4 • 2. H2O, heat • C) 1. O3 • 2. H2O, Zn • D) 1. BH3-THF • 2. H2O2, NaOH

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