Problem Set 4 - Key Due October 25, Suggest a plausible arrow-pushing mechanism for the following reactions. a. 1

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1 Problem et 4 Key Due ctober 25, uggest a plausible arrowpushing mechanism for the following reactions. a. 1 b. cat. l 3 65, 21 h 10 mol % , 1 h 85% 100% 3 3 A A 3 A A A 3 B Me 3 3 B b. Using the pk a s below, estimate the relative ratios of l/protonated lactone/protonated methanol at the beginning of the reaction.

2 l pk a approximate ratios ince Me is the solvent and present at around 20 moles/l, it will have about 20 times more of the protons than we estimate here The important point is that most of the protons reside on Me 2, not l. owever, since l is 10 5 more acidic, you can't predict which species is acting as the acid catalyst. Use A to symbolize the acid catalyst in your arrowpushing mechanism. 2. uggest a plausible arrowpushing mechanism for the following reaction. 2 Ts BF 3 BF 3 2 Me 0 BF 3 Ts BF 3 91% Me F 3 B Ts Ts Me Ts 3. uggest a plausible arrowpushing mechanism for the following reaction. 3 80% a tbu reflux, 24 h B Payne rearrangement the desired cyclization was not observed = 4. uggest a plausible arrowpushing mechanism for the following transformation. 4

3 cat. F l h 74% l l 3 l l l 3 3 B E B 3 5. uggest a plausible arrowpushing mechanism for the following transformation. 56 l l excess 3 a % 3 l l 3 l l l 3 3 B B 3 6. uggest a plausible arrowpushing mechanism for the following transformation. 7 a 87% 2 a 100, 6 h This is called the benzilic rearrangement

4 a a 7. uggest a plausible arrowpushing mechanism for the following transformation. 8 2 i) a, l 2 2, 80, 30 min % ii) aq. a 4 (workup) 2 2 l l 2 l B B 2 l 2 Ō 2 = B B 2 any order 2 workup 2 A 2 2 Additional Problems 8. uggest a plausible arrowpushing mechanism for the following transformation. 9 Ar 2 Me 3 BF l 2 / 2 23, 6 h Ar 2 BF 4 76%

5 Ar poorly soluble major oxonium ion in soln Ar Ar Ar 2 3 urprisingly, only 4% of the methyl product was obtained. 9. uggest a plausible arrow pushing mechanism for the following reaction. 10 K 2 3 l 3 62, 24 h 10. uggest a plausible arrowpushing mechanism for the following transformation BF 3 2 l , 10 d 70% F 3 B 2 BF 3 2 BF 3 BF3 F 3 B F 3 B A I can't rule out an alternative mechanism via. F 3 B

6 The full text version of Advanced rganic hemistry. Part A tructure and Mechanisms, 5th Ed. Francis A. arey and ichard J. undberg is available on line at http// I recommend that you also work these additional problems in arey and undberg, 5 th Ed. hapter 4 (ubstitution) 4.2, 4.3, 4.13, 4.17 eferences 1 ook, yril; Liron, Frederic; Guinchard, Xavier; oulland, Emmanuel J. rg. hem. 2012, 77, Klunder, J. M.; nami, T.; harpless, K. B. J. rg. hem. 1989, 54, Jung, M.; levenger, G. L. Tetrahedron Lett. 1991, 32, ubrata Ghosh, Debasis Patra A convenient route to vicinally substituted cyclopentanones via pinacol type rearrangement of cyclobutanes Tetrahedron Lett. 1993, 34, Jean M. onia, Jacques. alaun yclobutane ring contractions not involving carbonium ions Acc. hem. es. 1972, 5, Alfred assner, Vernon. Fletcher A new rearrangement in the reaction of α,αdihalocyclobutanones with base. Tetrahedron Letters 1970, 11, Ballard, D. A.; Dehn, W. M. Benzilic Acid rg. ynth. 1921, 1, Keith A. Monk and am. Mohan The ofmann earrangement Using ousehold Bleach ynthesis of 3itroaniline J. hem. Educ. 1999, 76 (12), p Vartak, A. P.; rooks, P. A. A calable, Enantioselective ynthesis of the α2adrenergic Agonist, Lofexidine rg. Process es. Dev. 2009, 13, emner, J. B.; own, E. J.; hohan, V.; Yates, B. F. Aust. J. hem. 1984, 37, harles Fehr A ovel Threearbon ing Expansion equence ynthesis of Exaltone and (±)Muscone elvetica himica Acta 1983, 66, ,