Chem 634Exam 2December 16, 20053 hoursProf. FoxYour Name_______________________________HHHHabOMeOcOdO1. Provide reagents for the following transformation. More than one step may be required.Do not write mechanisms.8 parts, 2 points eachQuestion 1 continuedeOHOHOHOfOHOOHOHgOOHHhOHOHOH+Ph NH2+HOcat H+OHHNPh2. Provide an arrow pushing mechanism10 points3(a) The reaction of diene A with dienophile B is regioselective. Explain.OOMeOOEtOOMeOHHOEtABOOMeOAO–OMeO+A'When preparing your answer, consider that the methoxy 'deactivates' the top carbonyl throughresonance as shown below. You may assume that the resonance form A' is the dominating factorthat guides the regioselectivity.6 points3(b) The reaction of diene C with dienophile B is also regioselective. Explain.OOOEtOOHHOEtCBOMeOMe6 points3(c) The reaction of diene D with dienophile B displays opposite regioselectivity as compared to C. Explain.OOOEtOOHHDBOHOHOEtHint 1: disregard what you wrote in parts (a) and (b) of this question. It is overwhelmed by another effect.Hint 2: the phenolic hydrogen of D is acidic. Recall the effect that Lewis acids have on Diels Alder reactions10 points4. Circle the correct product. Explain your choice with a carefully drawn analysis of the transition state.BOO+PhOPhOHPhOHPhOHPhOHPhOHPhOHPhOHPhOH(R)15 points5. Propose a multistep synthesisO15 points6(a) Propose an arrow pushing mechanismOBrPhOPhHBrOAc1210 points6(b) When the reaction in 6(a) is carried out with enantiomerically enriched 1, the product 2 that is obtained is nearly racemic. Propose an explainationOBrPhOPhHBrOAc1297% ee4% ee12
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