Lecture 10 - CH 310 N T Th 2-3:30 LECTURE 10 Textbook...

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1 CH 310 N T Th 2-3:30 LECTURE 10 Textbook Assignment: Chapter 16 (cont’d) Homework (for credit): POW 5 posted- Today’s Topics: The carbonyl group- Wittig and Related Rxns Notice & Announcements: Exam 1– Available in Chem Office Note: Late Office Hrs are moved to 1-2 PM for rest of the semester Organic Lecture Series 2 Morphine Naloxone- Antagonist for acute opiate overdose Natrexone- Longer acting Antagonist Used for opiate & alcohol dependence Organic Lecture Series 3 Aldehydes Aldehydes And And Ketones Ketones
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2 Organic Lecture Series 4 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 5 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 Organic Lecture Series 6 3 2 2 2 - Li + H-CH 2 -PPh 3 I - - 2 -PPh 3 3 2 2 3 LiI Butane Butyllithium + + + + + 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 3 H 3 -I 3 P-CH 3 I Triphenylphosphine + + S N 2 Methyltriphenylphosphonium iodide (an alkyltriphenylphosphine salt) Phosphonium Phosphonium ylides
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3 Organic Lecture Series 7 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: decomposition of the oxaphosphatane CR 2 O CH 2 Ph 3 P 2 - :O 2 3 P OC R 2 3 PC H 2 - + An oxaphosphetane + A betaine 2 R 2 3 P 3 P= O R 2 C=CH 2 An alkene + Triphenylphosphine oxide Wittig Reaction Wittig Reaction Organic Lecture Series 8 O 3 P + Ph 3 P=O 2-Methyl-2-heptene + Acetone O H 3 PP h P h 3 Phenyl- acetaldehyde ++ + ( Z )-1-Phenyl-2- butene (87%) ( E )-1-Phenyl-2- (13%) O H OEt 3 P O O 3 Eth yl ( E )-4-phenyl-2-butenoate (only the E isomer is formed) + + Phenyl- acetaldehyde Wittig Reaction Wittig Reaction Resonance stabilized Wittig reagent: Organic Lecture Series 9 – some Wittig reactions are Z selective, others are E selective
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Lecture 10 - CH 310 N T Th 2-3:30 LECTURE 10 Textbook...

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