310-25 - Organic Lecture Series CH 310 N LECTURE 25...

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Organic Lecture Series 1 CH 310 N LECTURE 25 Textbook Assignment: Chap 20 (omit 20.3) Homework (for credit): POW 8 posted (Due Mar 28) Today’s Topics: conjugate addn; overview of conjugated dienes Notice & Announcements: XM 2 this week (check BB announcements for room #) Organic Lecture Series 2 Enolate Enolate Anions Anions and and Enamines Enamines Chapter 19
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Organic Lecture Series 3 Gilman Reagents Gilman reagents undergo conjugate addition to α , β -unsaturated aldehydes and ketones in a reaction closely related to the Michael reaction: O 1. (CH 3 ) 2 CuLi, ether, -78°C 2. H 2 O, HCl O 3-Methyl-2- cyclohexenone 3,3-Dimethyl- cyclohexanone CH 3 3 3 Organic Lecture Series 4 Gilman Reagents Gilman reagents are unique among organometallic compounds in that they give almost exclusively 1,4-addition – other organometallic compounds, including Grignard reagents, add to the carbonyl carbon by 1,2-addition 2 CuLi 2 Et 2 O, -78 o O 3 O 3 1) 2) HCl, H 2 O
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Organic Lecture Series 5 organolithium and Grignard reagents, on the other hand, are strong nucleophiles (bases), add rapidly to carbonyl groups, and give primarily 1,2-addition: PhLi OO - Li + Ph H 2 O HCl OH 4-Methyl-2-phenyl- 3-penten-2-ol 4-Methyl-3- penten-2-one + Phenyl- lithium 1,2 Addition 1,2 Addition Organic Lecture Series 6 2 1 2 3 4 2 2 1,2 1,2 vs vs 1,4 1,4 -Addition Addition
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Organic Lecture Series 7 Thermodynamic versus kinetic control Thermodynamic versus kinetic control C O C C Nu ROH CCC OH Nu: RO - O C C C O CC H C O - - - + - + + fast slow 1,2-Addition (less stable product) 1,4-Addition (more stable product) KINETIC CONTROL: THERMODYNAMIC CONTROL: Products determined by relative rates Products determined by relative stabilities Organic Lecture Series 8
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310-25 - Organic Lecture Series CH 310 N LECTURE 25...

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