216 W09-Expt 7 - 216 Winter 09 Notes Dr Masato Koreeda Topic_Experiment 7 page 1 of 2 Date March 5 2009 Experiment 7 The Wittig Reaction[see Eges

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216 Winter 09 Notes - Dr. Masato Koreeda Date: March 5, 2009 Topic : _Experiment 7 ___ page 1 of 2. Experiment 7. The Wittig Reaction [see Ege’s: Section 21C (pp 869-872)] Georg Wittig P H 3 C Br P + CH 3 Br - phosphonium salt methyltriphenylphosphonium bromide benzene Δ (1) Reactive Ylides (Unstable) Ph P + Ph Ph C Li H 2 C CH 3 slightly acidic H H H Br - Ph P Ph Ph C H H Li + Br - Ph P Ph Ph C H H H 3 C CH 3 + + complete octet resonance stabilization involving a 3d orbital of P with a 2p on C " Unstable and Reactive " 10 bonding electrons on P Ylide or phosphonium ylide note: R' C R O complete octet sextet R R' C O not an ylide! Reaction of a reactive ylide with an aldehyde Ar-C(=O)H + Ph 3 P=CH 2 Ar-CH=CH 2 + Ph 3 P=O Mechanism: H O δ + δ - δ + δ - P CH 2 Ph Ph Ph O C C P Ph Ph Ph [2 π + 2 π ] cycloaddition concerted, one-step process oxaphosphetane intermediate C C H P O Ph Ph Ph + H H + enantiomer H cycloreversion H H P O Ph Ph Ph resonance stabilized triphenylphosphine oxide 4-membered ring!
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This note was uploaded on 01/31/2010 for the course CHEM 216 taught by Professor Nolta during the Winter '07 term at University of Michigan.

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216 W09-Expt 7 - 216 Winter 09 Notes Dr Masato Koreeda Topic_Experiment 7 page 1 of 2 Date March 5 2009 Experiment 7 The Wittig Reaction[see Eges

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