Epoxidation of Alkenes 1

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

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

Give the IUPAC name, including stereochemistry, for disparlure. cis-2-Methyl-7,8-epoxyoctadecane 5

Epoxidation of Alkenes RCOOH C + peroxy acid C O + RCOH 6

Example + CH3COOH O (52%) + CH3COH O 7

Stereochemistry of Epoxidation RCOOH C + syn addition C O + RCOH 6

Give the structure of the alkene, including stereochemistry, that you would choose as the starting material in a preparation of synthetic disparlure. Is disparlure chiral? H Disparlure is chiral peroxy acid O H 9

Epoxidation of cis-2-Butene R S RCO3H S R meso syn addition to cis-2-butene gives meso diastereomer 4

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 4

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 it more “electron rich.” 6

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

Ozonolysis has both synthetic and analytical applications. 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 15

Ozonolysis of Alkenes First step is the reaction of the alkene with ozone. The product is an ozonide. C C O + O3 17

Ozonolysis of Alkenes C C O + O3 H2O, Zn C O C O + Second step is hydrolysis of the ozonide. Two aldehydes, two ketones, or an aldehyde and a ketone are formed. C C O + O3 H2O, Zn C O C O + 17

Ozonolysis of Alkenes C C O + O3 (CH3)2S C O C O + As an alternative to hydrolysis, the ozonide can be treated with dimethyl sulfide. C C O + O3 (CH3)2S C O C O + 17

Example CH3 CH2CH3 H C 1. O3 2. H2O, Zn (38%) (57%) CH2CH3 C O CH3 H + 19

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

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

Introduction to Organic Chemical Synthesis Planning Reaction Steps & Linking Reactions MUST have a command of many reactions 1

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

Example: trans vicinal diols

Question Which reagent(s) will produce the product in the following reaction? A. KMnO4, NaOH, cold B. 1) OsO4, pyridine 2) NaHSO3, H2O C. 1) MCPBA 2) H3O+   D. OsO4 (catalytic), NMO E. all of the above  

Retrosynthesis

Prepare cyclohexane from cyclohexanol devise a synthetic plan reason backward from the target molecule always use reactions that you are sure will work 6

Prepare cyclohexane from cyclohexanol Pt 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?" 6

Prepare cyclohexane from cyclohexanol Pt 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?" 6

Prepare cyclohexane from cyclohexanol H2SO4 heat H2 Pt Alkenes can be prepared by dehydration of alcohols. The synthesis is complete. 6

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

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.

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

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