Chem 634 Exam 2 December 16 2005 3 hours Prof Fox Your Name 1 Provide reagents for the following transformation More than one step may be required Do not write mechanisms 8 parts 2 points each a b H H H H OMe O c O d O Question 1 continued e OH OH O OH f OH O OH OH O g O H H OH h OH 2 Provide an arrow pushing mechanism Ph OH OH HN cat H Ph NH2 O H 10 points 3 a The reaction of diene A with dienophile B is regioselective Explain O O OEt MeO MeO O O H H OEt B 6 points A When preparing your answer consider that the methoxy deactivates the top carbonyl through resonance as shown below You may assume that the resonance form A is the dominating factor that guides the regioselectivity O O MeO MeO O O A A 3 b The reaction of diene C with dienophile B is also regioselective Explain OMe O OEt O O C OMe O B H H OEt 6 points 3 c The reaction of diene D with dienophile B displays opposite regioselectivity as compared to C Explain OH O OEt O O O D OH B H OEt H 10 points Hint 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 reactions 4 Circle the correct product Explain your choice with a carefully drawn analysis of the transition state O O B R 15 points Ph O OH OH OH Ph OH Ph OH Ph Ph Ph OH OH Ph Ph OH Ph 5 Propose a multistep synthesis O 15 points 6 a Propose an arrow pushing mechanism Br HBr OAc Ph O 1 Ph O 2 10 points 6 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 explaination 12 points Br HBr OAc Ph O 1 97 ee Ph O 2 4 ee
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