R or S? oxidation #: hybridization:

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2 Remember Lone pair-assisted ionization. ame 15 F07-Exam o. 1 Page I. (0 points) The following compounds are those used in our study on the enzymatic transformation of cholesterol to pregnenolone. 1) Designate in each of the boxes below the stereochemistry (R or S) at the indicate carbon center and ) provide in each of the boxes provided the formal oxidation number of each of the indicated carbon atoms in pregnenolone. 1) stereochemistry (R or S) of the designated carbon centers: ) oxidation numbers of the designated carbon atoms: pregnenolone II. (10 points) Write in the boxes below the expected hybridization of each of the indicated atoms (i.e., sp 3, sp, or sp) in the following molecules. III. (10 points) For each of the following pairs of compounds, predict which compound is more acidic. Compare the two underlined s for each pair and circle the compound that is more acidic for each pair. (1) () a. ( 3 C) 3 C- b. 3 CC - a. F 3 CC - b. 3 CC - () a. b. 3 C - (3) a. b. - (5) a. b.

3 Remember Lone pair-assisted ionization. ame 15 F07-Exam o. 1 Page 3 IV. ( points) Dimethyl tartrate is widely used as a versatile starting compound in synthesis. In most of its application, the first step is the protection of the diol in dimethyl tartrate as its ketal. For example, treatment of dimethyl tartrate with excess cyclopentanone in the presence of a catalytic amount of p-toluenesulfonic acid (p-ts; pka -0.51) results in the formation of its cyclopentylidene derivative shown below. Draw the structure of the expected hemiketal intermediate and propose in the box below a curved-arrow reaction mechanism for this transformation from the diol to the cyclopentylidene ketal. You may use -B and B- for the acid p-ts and its conjugate bas, respectively. You do not need to balance each step. 3 C 3 C + -B 3 C 3 C dimethyl tartrate cyclopentanone cyclopentylidene (ketal) derivative (i) Draw the mechanism through the formation of the hemiketal intermediate. + 3 C 3 C (ii) Draw the mechanism through the formation of the ketal product. hemiketal intermediate 3 C 3 C ketal product

4 Remember Lone pair-assisted ionization. ame 15 F07-Exam o. 1 Page V. (1 points) 1) Azide ion ( - 3 ) is an excellent nucleophile that displaces a leaving group from primary and secondary alkyl halides and sulfonates. Show in the box provided below three major resonance forms of azide ion in Lewis structures. ) In a recent publication (rg. Lett. 007, 9, 069), azide ion was employed in order to stereospecifically introduce a nitrogen group as shown below. Provide in the box below the structure of the expected product from the following two-step reaction. Make sure to indicate its stereochemistry MsCl (C C 3 ) 3 C Cl 0 C. a 3 DMF (solvent) 80 C C VI. (1 points) Complete the following reaction scheme by providing the structures in each of the three boxes below (Synlett 007, 58). Ph 1. Cl C Cl Cl S Cl. (C C 3 ) 3 Ph 3 CC(=) (acetic acid) ClC C Cl (solvent)! (heat)! Ph Ph + K-C(C 3 ) 3 Cl ab[c(=)c 3 ] 3 imine + KCl + C(C 3 ) 3

5 Remember Lone pair-assisted ionization. ame 15 F07-Exam o. 1 Page 5 VII. (18 points) Complete the following reaction schemes by providing in the boxes the structures of the corresponding products. Make sure to indicate the stereochemistry and, where applicable, label isotopes. 1). My work from the last century! C 3 a C 3 C 3 insect juvenile hormone 18 Cl (catalytic) 0 C ) [Eur. J. Chem. 005, 99] Br Mg 1. TF (solvent). aq Cl 3 +,! + C membered hemiacetal + enantiomer

6 Remember Lone pair-assisted ionization. ame 15 F07-Exam o. 1 Page 6 VIII. (16 points) Complete the following reaction schemes by providing in the boxes the structures of the corresponding products. Make sure to indicate the stereochemistry where applicable. (1) Br dioxane (solvent) + () 1. 9-BB. / a Cr 3, S, acetone

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9 The Reagent List Page 9 Shown below is a list of key reagents (not always the whole recipe) that may be useful for solving questions on the exam #1. reagent classification or specialized use From Chem 10 s oxidation KMn oxidation peroxyacid epoxidation (e.g., 3- or meta-chloroperoxybenzoic acid) i. 3 ; ii. (C 3 ) S or Zn ozonolysis i. 3 ; ii. ozonolysis a base, nucleophile a base KC(C 3 ) 3 bulky base /Pd hydrogenation /Pd, BaS, quinoline hydrogenation i. B 3 or 9-BB; ii., a hydroboration PBr 3 e.g., R- R-Br SCl e.g., R- R-Cl p-c 3 C 6 S Cl (p-tscl) tosylate formation C 3 S Cl (MsCl) mesylate formation -bromosuccinimide (BS) Br source of electrophilic Br ========================================================================= Chapter 13 C ClCr 3 - (PCC) oxidant Cr 3 / S / /acetone oxidant i. ClC(=)-C(=)Cl, (C 3 ) S; ii. (C C 3 ) 3 oxidant Chapter 1 ab nucleophilic hydride LiAl nucleophilic hydride diisobutylaluminum hydride nucleophilic hydride (DIBAL) RMgX nucleophilic carbon RLi nucelophilic carbon -C 3 C 6 S 3 (p-ts) Raney i SC C S BF 3 (C C 3 ) organic-soluble acid Lewis acid desulfurization thioacetal/thioketal formation hydrazone formation oxime formation