Solns1-13-06

Solns1-13-06 - CHEM 252 HONORS ORGANIC CHEMISTRY II Spring...

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Unformatted text preview: CHEM 252 HONORS ORGANIC CHEMISTRY II Spring 200 Dr. David Jl. Lapinsky 1/13/06 Problem Session: Review of some things from CHEM 251 1.) Suggest a mechanism to account for the following reaction and predict which diastereombr would be the major product. Br Me Br2 + l M 9 Br 9 Br H 1 A B 2.) Draw th expected products when optically active (FI)-3-isopropyl-1- methylcycl hexene is treated with Br2/H20. Do you expect these products to be optically ac ive? Do you expect an equal distribution of the products? If not, identify thelmajor product. 3.) Suggest a reasonable mechanism to account for the following reaction. Br2 0 Br W0 H —-—-> 4.) The foll wing is an example of a process known as iodo-lactonization. Based on your kn wledge concerning halogenation of alkenes, propose a mechanism for this reaction. Which product, A or B, has the expected stereochemistry? Explain. o I o 2 ——-—-> OH NaHCO3 @ I o o 0 or QC: ' B m A 5.) Terpin iT a compound that exhibits expectorant properties and is used as a constituent in various cough medications. OH / OH Terpin (F?) a) Starling with optically active (R)-limonene, propose a synthetic route to terpih. b) Howl many stereoisomers of terpin are possible? Draw all the possibilities. c) Draw the expected major isomer produced in your synthesis. d) Is terpin expected to be optically active? Briefly justify your reasoning. 6.) The following carcinogenic diol epoxide is formed when liver enzymes attempt to metabolize benzo[a]pyrene, a polyaromatic hydrocarbon found in cigarette smoke and auto exhaust. This epoxide survives long enough to react with some nucleophilic sites of DNA causing mutations. Among these reactions is the one that occurs between the C(2) nitrogen (boxed) of a guanosine residue—one of the bases of DNA—and the epoxide. Draw the possible products oflthis reaction and indicate the relevant stereochemistry in each case. (Hint: These reactions are analogous to those involving epoxides and H0' anions.) ' E liver 7 -——-———> enzymes V HO‘ O I Guanine residue GUanIne </N I NH ofDNA l NW ribose 7.) Diisopinpcampheylborane [often abbreviated as (lpc)ZBH] is a useful reagent for the enantioselective hydroboration of alkenes. This reagent is derived from optically active a-pinene. Draw the structure of diisopinocampheylborane and propose a mechanism for the formation of diisopinocampheylborane from BH3 and a-pineme. CH3 H30 .— H30 a-pinene 8.) Many biologically important processes may be classified as 8N2 displacement reactions. For example, nature uses SAM (S—adenosylmethylthionine) for various biological methylation reactions. a) Use the arrow formalism and draw a mechanism for the formation of adrenaline (epinephrine) from norepinephrine and SAM. NH2 NH2 /N \ N Ho H020 < l J HO OH + N N OH HO + IS 0 B ; HO NH2 H30 W‘ rim OH CH3 Norepinepliirine SAM Epinephrine (adrenaline) b) Use the arrow formalism and draw a mechanism for the formation of the important lipid phosphatidylcholine from phosphatidylethanolamine and SAM. i? f? RO-IID-OCHzCHzNHz RO-lf-OCH20H2N(CH3)3 O- O- Phosphatidylethanolamine Phosphatidylcholine Z ‘ P(<‘k«‘%fl"= Sag-Jon Q 3 S+EUQOUY \o\oc\<5 I ‘FQQQ boHam (at? aAén. ' F“ e” ( <59 Rd W *1 Br: 6 r‘ r 5‘ ® »‘\‘j x mas o r\ S’fEfLLII‘HY’I , , ,. b‘aLK5 +o‘ Faga a' \ +oc 'thl (m JOKJ e E) ( acidn \ a & r® (An .I ll,” Qtidfl « 0“ (5r ® a} OH a OH ’ d ;a5%ueomc:,t s (fwom bcH'l-H‘O ...
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This note was uploaded on 05/03/2008 for the course CHEM 252 taught by Professor Billups during the Spring '08 term at Rice.

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Solns1-13-06 - CHEM 252 HONORS ORGANIC CHEMISTRY II Spring...

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