Ch_322b_17.07

Ch_322b_17.07 - Chapter 17.7 lecture note

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Additions to ! , " -Unsaturated Aldehydes and Ketones C=C-C- :O: = C=C-C- :O: : + - C-C=C- :O: + - C C C O !" ! + ! + Nu: - modes of nucleophilic attack ! , " -Unsaturated aldehydes and ketones react with nucleophiles by simple (1,2) addition, and/or conjugate (1,4) addition. These two modes of reaction are understandable from an examination of the resonance structures for a conjugated enone system that shows two electropositive carbon centers .
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Reaction Schemes for Simple and Conjugate Additions C=C-C- O = + Nu: - +H + simple addition (1,2-addition) +H + conjugate addition (1,4-addition) C=C-C- O- H Nu C-C=C- O- H Nu enol (initial product) C-C-C- Nu O H ketone
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Examples Often both modes of addition compete giving a mixture of 1,2- and 1,4-addition products. CH 3 CH=CHCCH 3 O = (i) CH 3 MgBr (ii) H 3 O + 3-penten-2-one CH 3 CH=CHCCH 3 CH 3 OH + CH 3 CHCH 2 CCH 3 O CH 3 1,2-addition product 72% 1,4-addition product 20% While Grignard reagents give mixtures from both addition modes, organocopper reagents tend to give conjugate addition products. O
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This note was uploaded on 10/20/2009 for the course CHEM 322BL at USC.

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Ch_322b_17.07 - Chapter 17.7 lecture note

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