PhCHO. TsOH, etc. TsOH, etc. 1) NaH, etc H 3 O + 2) PhCH 2 Br, etc 2/3. NaBH 3 CN HCl. 1 equivalent of TsCl/py 1) C , DMSO

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1 W Exam No. 3 Page 1 I. (40 points) J. rg. hem. 2004, 69, 113 ustomized synthesis of carbohydrate compounds is a popular area of research. omplete the following steps, as required, from a recent report, which begins with a (D)-glucopyranose. 3 Ts, etc Ts, etc A 3/2 B 3/ equivalent of Tsl/py E D NaB 3 N l 3 1) Na, etc 2 Br, etc 2/3 Ts 3 2 pts for wrong R, of both, or forming Rl F 3 1) l, DMS l ( 3 2 ) 3 N (Swern reaction) 3 NaN 3 NaB 4 3 N 3 K if consistent 3 stereoselective formation of an isomer of compound F 3

2 II. (30 points) J. rg. hem. 2004, 69, 113 W Exam No. 3 Page 2 A. The chemistry in Problem 1 was reported as part of some studies on the antimicrobial agent named neomycin. Provide the balanced equation for the complete acid hydrolysis of neomycin. Stereocenters where there is a mixture of stereoisomeric products should be indicated with a "squiggly" line: 2 N Neomycin N 2 N 2 2 N N 2 3 N 2 N 2 B. The anomeric effect provides a way to rank the following three isomers. N 2 NTE: products should be shown in their acid/base uncharged forms; that is, any amine groups should be -N 2 rather than -N 3 +, and alcohols should be -. N 2 N 2 N 2 structure = 3 stereo = 2 N 2 20 W X Y Ranking: least stable intermediate most stable Y W X provide an explanation for the ranking: The anomeric effect makes an electronegative atom group in the axial position (with respect to another electronegative atom at that same carbon) more stable: in compound X, both of the oxygens is in an axial position with respect to the other one as the ring of reference; in compund W, only one of oxygen atoms is axial with respect to the other, while the other is equatorial; basic idea = 3 in compound Y, both are equatorial complete idea = 2

3 W Exam No. 3 Page 3 III. (30 points) Rudolf Diesel introduced a new type of engine at the 1898 World's Fair. The newly emergent petroleum industry in the U.S. had not yet become a powerhouse, so Diesel was a strong advocate for foodstuffbased fuels. In particular, Diesel used fatty acid esters derived from reacting vegetable oils with alcohols under catalytic base conditions. These esters, called "biodiesel fuels," were recently re-examined by the US Department of Energy and the US FDA, who found that these compounds have 3.2 times the energy content than typical fossil fuels. (a) provide the balanced equation for the following: excess 3 catalytic 3 Na 9 (b) Provide a complete, step-wise mechanism for the formation of the first ester that forms (you may select which one that is). The reaction mechanism should illustrate the catalytic nature of the 3 Na in the process (NTE: If you need to, you may purchase the answer to part (a) from your GSI) pt (2 pt for alkoxide/s) 3 4 pt, 1 for stoichiometry 3 3 mech =4 struct =2 mech = struct =2 struct =2 mech =4 3 + methoxide =2 R =1 21

4 IV. (20 points; J. rg. hem , 130) W Exam No. 3 Page 4 A. There are two stereoisomeric products in the following photochemical cycloaddition reaction; draw one of them. 3 connectivity = 4 stereochem = 3 (can be all cis) 3 3 light 3 B. Thee following cyclobutene molecule undergoes an electrocyclic ring opening to give major and minor stereoisomeric products. Draw the structure of the major product. 3 3 heat 3 3 connectivity = 4 stereochem = When the optically active tetrose (D)-erythrose is chemically converted to an epimeric pair of optically active pentoses, (D)-ribose and (D)-arabinose. When asked about the simplest possible experiment to determine which is which, experienced chemists will say: "All I need is some sodium borohyride, and then to carry out a simple measurement." ow does this answer so easily the question of which pentose is which? (D)-erthyrose (D)-ribose (D)-arabinose optically inactive optically active 6

5 V. (20 points) omplete the following reaction sequences, as necessary. W Exam No. 3 Page 1) Sl 2 connectivity = 3 stereochem = 2 1) Li Br 3 3 connectivity = 3 stereochem = 2 3 N 2 N 3 no partial 3 1) Sl 2 3 / All 3 no partial 3