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Spring 06 Exam 6 Key - CHEMISTRY 225(24(23 TEST#6 1 ‘1 2...

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Unformatted text preview: CHEMISTRY 225 (24) (23) TEST #6 JUNE 23, 2006 1. ‘1 2. NAME w you t. ./ (L7 3. (16) 4. TOTAL GOOD LUCK! l. (24 Points) ORGANIC REACTIONS. Complete SIX of the following organic reactions by providing structures for the reactant, product, or reagent as required. Be sure to Show stereochemistry andfor regiochemistry in cases where such characteristics are important. If no reaction is expected under the reaction conditions, write “N.R.” and explain briefly why the reaction fails. If you complete more than six equations, please indicate clearly whichfour you wish to have graded. \\OCH2Ph = 1. BH3.THF mm)» 2. H202, OH_(aQ) R0 2.7-— Org. Left. 2086, 8, 2429 H H CH3 Br 2M CH3CH20‘ ........ fin, D CH3CH20H D E 2.— (- H 5v, woic (major product) _(12) (75) HO 0(C H3)3 Si(CH3)3 Org. Lett. 2006. 8. 2507 2. (CH3)28 GEE“ 3 CH3 OCH3 3 2. (23 Points) STRUCTURE, REACTIVITY, AND REACTION MECHANISM. a. ( I f 6) Write a detailed, stepwise reaction mechanism to account for the following hydration reaction. A complete reaction mechanism will include structures for all intermediates and curved mechanistic arrows to represent the “flow” of an electron pair. HO CH3 ..., HP 4. 10H. ” N 1% ’3 OhIL. a, I ("9 _-> l/efi *——> I , . H V . H- b. ( f 4) Would a single alcohol product be obtained if the hydroboration sequence were applied to compound A above Why or why not? You may write an equation to support yfiroeiplan’eiiiit? blvv—e ‘I—kxaaii7 IG'C wt‘v‘Z [Dv'oit‘luoi‘z- Wt” L4 "JC~-~*’C’I flunk” Lu“: lav-([4— flit/Le (1‘0“th Lauri out Q MRI (—x-LLI-vI- IM‘IJ- ‘11.; I; 410%— Gave-- 649*! I,— ‘i-0 e‘ V QMFI Wm)“. £?wai [DWLa 4L 0L5_ c( K“) o (4) Compound A can be produced in a regioSpecific fashion from secondary cycloalkyl halide B (equation l to the right). Account for the fact that only a single cycloalkene product is formed in this reaction. 1;“ m about WW1” a» :1 air In‘ll. hf]; Cg _ as; ~— L1 0 U-I - "I‘O ‘flH—a- \W‘? W" we 4 o (7) Complete the additional reactions of compound B with structures for the products. CH3 _I,Br B ———>- CH3CH20H d. ( i 2) Write a structure for the cationic intermediate in the electrophilic bromination of cyclohexene. 3. (16 Points) CURRENT EVENTS (ALKENE REACTIONS TN THE NEWS) a. ( i S) The reaction below involving two carbocationic intermediates was described recently by Japanese chemists [Tetrahedron Lett. 2006, 47, 4145]. FE,- H —n- H3C I —h- roducts H30 {2 PCHs ch OCHa H c (9 OCH3 p 3 OCH H30 3 ch C OCH3 D OCH3 o (3) Carbocation rearrangements normally produce a more stable cation On the grounds of structure and bonding account for the fact that cation D is more stable than cation C. c Cain.» M3 {Maui-i7 via;- 4a,.”(i ”at“. m c at. L to... a -thww Ml J a VL— ® (“Lolit- ’0“ 3 Cam in: viieivojiu- @m'l' i0 L’O'fle 0?!— L7 «en/awawct 0a; 0 (2) Suggest the structure of an alternate carbocation that might have been all; a up formed in the initial protonation step. alternate carbo'cation 5 b. ( r 3) Prof. K. Barry Sharpless shared the Nobci Prize in Chemistry in 2001 for develOping the asymmetric epoxidation reaction that now bears his name (the Sharpless epoxidation). The Sharpless epoxidation was utilized by German chemists as the first step of the total synthesis of the natural antibiotic (— )— 8— O- -rnethyltetrangomycin {Org Lerr. 2006 8_._ 250?]. The product E below was formed from geraniol 1n 91% enantiomeric excess. W O OH .A E l . 39396916., J ”’35 Y / \l / geraniol enantiomeric product 0 (3) Write a structure for geranio], the aliylic alcohol precursor to this cpoxide product. a [2, BONUS QUESTION). Write a structure for the enanriomeric product that would have been formed in low yield in this epoxidation reaction. c. ( I 5) Eugenol, the principal organic component ofthe oi] ofcloves, is this week’s Molecule of the Week at the American Chemical Society website. Complete the two reactions of eugenol below. 1 Hg(o_A_c)2, H20 2. NaBH4 CH30 HOK; %CHQCH: CH2 eugenol c. ( f 3) Chemists at the National Chemical Laboratory in Pune, India have recently developed a chiral synthesis of the unusual amino acid B-hydroxyornithine [Tetrahedron Lerr. 2006, 47, 4167]. Among the steps in the synthesis was a dihydroxylation reaction which resulted in a syn addition of two hydroxyl groups to a double bond. o I: 0‘46 u Et&M\/V\/\OE t h dioi product || reagents RHN/WAOEt I (3) Complete the equation above with a structure for the product that shows its stereochemistry clearly. . (3, BONUS QUESTION!) A subsequent step in the synthesis of B-hydroxyornithine is shown below. By what mechanism is this reaction taking place? How can you tell? érJZ ‘A ”Lick HLlW-Dw Lott, OCGUVVEA Q «Lic— '2 04':th to in site w... e N; i;- cc Corgi mur- cl, Lita 0%; flLLLiL LlefQ‘t-n- «rm eccuwv/ W1 ‘u~CV{-f©~— 4. (12 Points) MULTIPLE CHOICE. ¢ Circle the reagent that converts a primary alkyl halide to an alkene; underline the reducing agent NaBH.; -0 H‘ KMnO4 - Circle the compound in which the indicated carbon is in the lowest oxidation state; underline the compound in which the indicated carbon is in the highest oxidation state. / ' J 0 Q3 OCH3 - Circle an intermediate in hydroboration of l-butene; underline an intermediate in the acid— catalyzed hydration of l-butene. . ”.5 I _. ' - (Er) CH3'CHQCHQCHZBH2 0ch HZCHZCHQOHQ CHSCHchc H3 CH30H20H0H3 BH2 00H2 E 9% Which of the following reagents would NOT be classified as an electrophile towards the carbon- carbon double bond? A. Brz B. CHaBr C 82H6 D. HOBr 1; Account for the fact that electrophilic addition of HBr(g) to 2-methylpropene (isobutylene) produces only 2-bromo~2-methylpropane (terI-butyl bromide). A. The reaction proceeds by way of a bridged bromonium ion. B. The hydrogen adds so as to form the most stable carbocation. C. Bromine is a large atom so it prefers to attach to the least congested carbon. D. The initially formed primary carbocation rearranges to the more stable tertiary carbocation. A The anti orientation of two bonds is important in organic reactivity. Which of the following statements is FALSE? A. In a catalytic hydrogenation reaction the two hydrogens are added anti to each other. B. The two departing groups must be anti in an E2 reaction. C. Addition of bromine to an aikene in methanol results in anti addition of bromine and methoxy. D. In the 8N2 reaction the nucleophile forms a bond anti to the leaving group. ...
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