Lecture 10 given Sp 09 - Wittig Reaction: New C-C bond...

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Wittig Reaction: New C-C bond formation--essentially the reverse of ozonolysis Georg Wittig 1897-1987 Shared the Nobel Prize with H.C. Brown in 1979
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ittig Reaction Wittig Reaction • The Wittig reaction is a very versatile synthetic method for the synthesis of alkenes from aldehydes and ketones. • A simple example, before we talk more generally: + + - + CH 2 Ph 3 P= O 3 P- 2 O Triphenyl- phosphine oxide Methylene- cyclohexane A phosphonium ylide Cyclohexanone
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The Wittig Reaction The Wittig reaction is a very versatile synthetic method for the synthesis of alkenes from aldehydes and ketones. + A R •• (C 6 H 5 ) 3 P C + C O ' •• “ylide” B R ylide R A + •• + C C R' B (C 6 H 5 ) 3 P O •• New C-C bond formation--essentially the reverse of ozonolysis
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Phosphonium Ylides p Ylide : a molecule which, when written in a ewis structure showing all atoms with Lewis structure showing all atoms with complete valence shells, has positive and negative charges on adjacent atoms (it is gg j ( a subset of what are called zwitterions) + hosphonium ylides re formed in two (C 6 H 5 ) 3 P CH 2 Phosphonium ylides are formed in two steps: . treatment of triphenylphosphine with a 1 ° r 1. treatment of triphenylphosphine with a 1 or 2 ° alkyl halide to form a phosphonium salt followed by 2. treatment of the phosphonium salt with strong base, typically butyl lithium
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hosphonium Ylides Phosphonium Ylides •P h osphonium ylides re formed in two steps: osp o u y des a e o ed t o steps – Step 1: Nucleophilic displacement of iodine by triphenylphosphine. – Step 2: Treatment of the phosphonium salt with a very strong base, most commonly BuLi, NaH, or NaNH . 2
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ittig Reaction Wittig Reaction • Phosphonium ylides react with the C=O group of aldehydes and ketones to give alkenes.
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Lecture 10 given Sp 09 - Wittig Reaction: New C-C bond...

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