318-12 - Organic Lecture Series CH 318 N LECTURE 12...

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Organic Lecture Series 1 CH 318 N LECTURE 12 Textbook Assignment: Chapter 16 cont’d Homework (for credit): POW 6 posted Today’s Topics: Aldehydes/Ketones-reactions Notice & Announcements: Organic Lecture Series 2 Aldehydes Aldehydes And And Ketones Ketones
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Organic Lecture Series 3 The Wittig reaction is a very versatile synthetic method for the synthesis of alkenes (olefins) from aldehydes and ketones Triphenyl- phosphine oxide Methylene- cyclohexane A phosphonium ylide + + - + CH 2 Ph 3 P= O 3 P- 2 Cyclohexanone O Wittig Reaction Wittig Reaction Ph 3 PC H 2 Ph 3 P CH 2 Ylides are reagents (or reactive intermediates) which have adjacent charges: Organic Lecture Series 4 O Ketone Can Be Cyclic C Alkenes or Olefins R' R Overall Synthetic Transformation of Overall Synthetic Transformation of Wittig Reagents & Its Variations Wittig Reagents & Its Variations
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Organic Lecture Series 5 Phosphonium ylides are formed in two 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 Ph 3 PC H 3 -I 3 P- CH 3 I Triphenylphosphine + + S N 2 Methyltriphenylphosphonium iodide (an alkyltriphenylphosphine salt) CH 3 2 2 2 - Li + H-CH 2 -PPh 3 I - - 2 3 3 2 2 3 LiI A phosphonium ylide Butane Butyllithium + + + + + Phosphonium Phosphonium ylides ylides Organic Lecture Series 6 Phosphonium ylides react with the C=O group of an aldehyde or ketone to give an alkene Step 1: nucleophilic addition of the ylide to the electrophilic carbonyl carbon Step 2:
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This note was uploaded on 10/10/2010 for the course CH 57689 taught by Professor Goddard during the Spring '10 term at University of Texas.

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318-12 - Organic Lecture Series CH 318 N LECTURE 12...

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