APTER 20 W: ARBNYL REDX RXNS YDRIDE REATIN MEANISM 1. Give the curved arrow mechanism for each reaction. LiAl 4 NaB 4 3 2 YDRIDE REATINS 2. Give the major organic product(s) for each reaction. Indicate if a racemic mixture is expected. NaB 4 3 2 LiAlD 4 LiAl 4 d. 3 NaBD 4 3 2 D Page 1
AETYLIDE REATINS 3. Give the reagents needed for each step in these syntheses. RGANLITIUM + RGANMAGNESIUM MEANISM 4. Give the curved arrow mechanism for this reaction. Li RGANLITIUM + RGANMAGNESIUM REATINS 5. Give the major organic product for each reaction. Indicate if a racemic mixture is expected. 3 MgBr e. I Li (s) acetone + workup Li f. Mgl 3 MgBr g. MgBr D 2 Ph 3 2 Li d. h. l Mg (s) + workup Page 2
RETRSYNTESIS 6. Fill in the boxes with either reactant or reagent needed to complete each reaction. (ra) 3 MgBr d. Li 7. Why is it important that the reagents involved in an organomagnesium reaction (Grignard) be separated into steps (a+b)? 3 MgBr NT 3 MgBr + 8. Show two different methods for synthesizing this alcohol starting from an alkyl halide, and using a carbon-carbon bond forming reaction. Page 3
9. Design a synthesis of each compound, using reagents of 5 carbon atoms or less. Show all reagents and synthetic intermediates. 10. Design a synthesis of the compound below, using reagents of six carbon atoms or less. Show all reagents and synthetic intermediates. l Page 4
PRTETING GRUPS 11. None of diol A was obtained when attempting the following synthesis. Explain what may have gone wrong, and design a successful synthesis of diol A. Note: 1 equivalent means using equal molar amounts of the limiting reactant and the reagent. Br 1 equivalent of Mg (s) cyclohexanone + workup Diol A 12. Ethynlestradiol (in birth control pills) can be synthesized from estrone by reaction with two equivalents of lithium acetylide. 2 equiv. Li Estrone Ethynlestradiol Explain why two equivalents of acetylide are needed. Design a synthesis that uses only one equivalent of acetylide. Page 5
REATIN REVIEW 13. Give the reagents needed for each step in these syntheses. Note: many are old reactions. All chiral synthetic intermediates are racemi 3 Br Br d. TMS 3 TMS 3 e. l Na REATINS F α β UNSATURATED ARBNYLS 14. Use resonance structures and words to explain why an α β unsaturated carbonyl is reactive to nucleophilic attack at two regions. Page 6
15. Give the major organic product or reagent(s) for each reaction. 3 2 Li ( 3 ) 2 uli LiAl 4 d. uli 2 e. 3 2 MgI f. g. h. i. ( 3 2 ) 2 uli 3 2 Br j. Page 7
REATIN REVIEW 16. For this interconnected reaction scheme, Fill in the boxes with each intermediate (identify compounds A-K). PhMgBr con. 2 S 4 3 heat Zn LiAl 4 A B B l PBr 3 mpba D Mg 2 = + workup I Mg Ph + workup E 3 MgBr F K G What is the relationship between compounds F, G, and K? Are they identical, enantiomers, diastereomers, constitutional isomers or not related (not isomers)? Page 8
SYNTESIS PRBLEMS 17. Design a synthesis of each compounds, using reagents of 6 carbon atoms or less. Show all reagents and synthetic intermediates. Above each arrow shows the number of steps the transformation can be performed in, but you can use as many steps as you need. 2 2 3 N 2 d. 1-2 Page 9
17 continued e. 2 f. 4 Na g. 2 Page 10