Chem634_F11_PS05 - we have discussed the last two weeks...

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Chemistry 634: Advanced Organic Chemistry – Synthesis and Reactivity Fall 2011, University of Delaware Prof. Donald Watson Problem Set 5 Due Beginning of Class 11/15/11 You may work in groups, unless otherwise noted. No not try to fit answers on these pages, use separate paper. 1. Provide the missing reagents and provide mechanistic/stereochemical rationale for choices: TIPSO Me O Bu O H Me H single enantiomer 2. Predict the product, including stereochemistry. Draw a transition state model leading to the predicted product. a) Me O Me Me Bu 2 BOTf I Pr 2 NEt then PhCHO b) O O Me CHO PhO 2 C Me Me OPh O Me LDA (excess), then c) N O Me O O Bu 2 BOTf, i Pr 2 NEt, then CHO Me TBSO Me d) N O Pr O O Bu 2 BOTf, i Pr 2 NEt, then CHO Ph Me Bn e) TBSO Me O TBSO Me OPMB MeO OMe Me TiCl 4 , i Pr 2 NEt 3) The total synthesis of polyketides provides a classic example of the application of a lot the chemistry
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Unformatted text preview: we have discussed the last two weeks (much of this chemistry was developed for this purpose). A very nice example is Evans synthesis of ionomycin ( JACS , 1990 , 112 , 5290). Look up this paper and analysis the total synthesis. Provide a complete retrosynthetic analysis (note, copying Evans directly from the paper will win you no points I want more detail), and find all examples of protection/deprotection, alcohol/ketone oxidations and chiral. aux. asym. alkylations or substrate controlled alkylation, and aldol reactions. For the alkylation and aldol reactions, draw a transition state model for each reaction to explain observed stereochemistry. You may have to do more background reading for some of the aux. methods we did not discuss....
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