Lecture 24 Two Germans and an Englishman Robert Robinson 1886-1975 Nobel Laureate 1947 April 17, 2018 tto Paul Hermann Diels 1876-1954 Nobel Laureates 1950 Kurt Alder 1902-1958
Exam III Tomorrow Wed April 18 WEL 2.122 7-9 PM Covers thru today Homework Hydrolysis Reactions Synthesis Get an A!!!
A Confession
Electrophilic reactions of aniline the true story H 2 N Br 2, H 2 Br N H 2 Br Strong activator Br H 2 N H 2 N H 2 N HN 3 H 2 S 4, 20 o C + N 2 N 2 H + 51% 47% + H 3 N nitration
Protection-deprotection allows us to synthesize p-nitroaniline in a high yield N H 2? N H 2 Acylation N 2 Hydrolysis HN Nitration HN a weak base N 2
Enolate Anions When a ketone has two different -hydrogens, is formation of the enolate anion regio-selective? The answer depends on experimental conditions
There are other issues that you should now be prepared to consider.?
Kinetic Control with slight excess of LDA slight excess - Li + - Li + 0 C + LDA + + (i-pr 2 ) NH 2-Methylcyclohexanone 99% 1% fastest but least stable
Thermodynamic Control With slight excess of ketone slight excess + LDA 0 C - Li + - Li + 10% + + (i-pr 2) NH 90% Slow but most Stable
Kinetic Control When a reaction is under kinetic control, the composition of the product mixture is determined by the relative rates of formation of each product Thermodynamic Control When a reaction is under thermodynamic control, the composition of the product mixture is determined by the relative stabilities of each product
Which position is thermodynamic??? Why??
Michael Reaction Michael reaction: conjugate addition of an enolate anion to an, -unsaturated carbonyl compound!! Following are two examples in the first, the nucleophile is the anion of malonic ester in the second, it is the enolate anion of acetoacetic ester An excellent route to 1,5 dicarbonyl compounds
Michael Reaction EtC CH 2 + CH 2 =CHCCH 3 EtC 3-Buten-2-one (Methyl vinyl ketone) Diethyl propanedioate (Diethyl malonate) EtC Et - Na + EtH EtC CHCH 2 CH 2 CCH 3
Michael Reaction CH 3 C EtC CH 2 Ethyl 3-oxobutanoate (Ethyl acetoacetate) + 2-Cyclohexenone Et - Na + EtH CH 3 C EtC CH
Retro-synthesis of 2,6-Heptadione from acetoacetic formed in a ester Michael reaction CH 3 CCH 2 CH 2 CH 2 CCH 3 CH 3 CCH-CH 2 CH 2 CCH 3 lost by decarboxylation C 2 H CH 3 CCH 2 + CH 2 =CHCCH 3 C 2 Et Ethyl acetoacetate Methyl vinyl ketone Always gives a 1,5-dicarbonyl product
Michael Addition The Michael reaction is a useful method for forming carbon-carbon bonds.1,5 dicarbonyls 1 2 3 4 5
Michael Addition It is also useful in that the product of the reaction can undergo an intramolecular aldol condensation to form a sixmembered ring. ne such application is called the Robinson annulation. This reaction enabled the first synthesis of steroids
The Robinson Annelation: 1. Michael addition CH 3 + H 2 C CHCCH 3 KH, methanol CH 3 CH 2 CH 2 CCH 3
Robinson annelation: 2. aldol condensation CH 3 NaH CH3 heat CH 2 CH 2 CCH 3 H not isolated; dehydrates under reaction conditions
Robinson annelation: 3. elimination CH 3 NaH heat CH3 CH 2 CH 2 CCH 3 H CH 3 Robert Robinson
Testosterone Cortisone
The Signature Page Claisen Condensation: -ketoesters Dieckmann: Cyclic -ketoesters Aldol:, -unsaturated aldehydes and ketones Acetoacetic ester synthesis: decorated acetones Malonic ester synthesis: decorated acetic acids Michael Reaction: 1-5 dicarbonyl compounds Grignard Reaction: Alcohols Wittig Reaction: Alkenes., etc
The Diels-Alder Reaction tto Paul Hermann Diels 1876-1954 Kurt Alder 1902-1958
Diels-Alder Reaction: The Diels-Alder reaction is an addition reaction between a 1,3-diene and an alkene (called a dienophile), that forms a new six-membered ring.
Predict the products
All Diels-Alder reactions: 1. are initiated by heat; that is, the Diels-Alder reaction is a thermal reaction. 2. form new six-membered rings. 3. involve breaking three bonds and making two new bonds and one new bond. 4. are concerted; that is, all bonds are broken and new bonds formed in a single step.
4 Rules that govern the Diels-Alder reaction 1. The diene can react only from the s-cis conformation.
2. Electron-withdrawing substituents in the dienophile increase the reaction rate. The conjugated diene acts as a nucleophile and the dienophile acts as an electrophile. Electron-withdrawing groups make the dienophile more reactive If Z is an electron-withdrawing group, then the reactivity of the dienophile increases as follows: Chemistry 28 328N
Common dienophiles The carbonyl group is electron-withdrawing and activates dienophiles
Example H 2 C CHCH CH 2 + H 2 C CH CH benzene 100 C via: CH CH (100%)
3. The stereochemistry of the dienophile is retained.
Example C 6 H 5 CH H 2 C CHCH CH 2 + C C H H H only product H C 6 H 5 CH
Example H CH H 2 C CHCH CH 2 + C C C 6 H 5 H C 6 H 5 H only product H CH
H CCH 3 + C C CH 3 C H H CCH 3 H CCH 3
H CCH 3 H CCH 3 is the same as CCH 3 H H CCH 3
4. When endo and exo products are possible, the endo product is preferred. endo and exo indicate the orientation of Z. endo = on the side of the big bridge exo = on the side of the small bridge
The endo product is preferred!
Some nomenclature
Nomenclature of Bicyclic Systems Bicyclo [#.#.#]alkane Where # is the number of carbons on the bridges (in decreasing order) and the alkane name includes all the carbons in the compound.
Nomenclature of Bicyclic Systems Numbering begins at a bridgehead, goes around the largest ring first, to give the lowest number to any functionality on the ring. 5 4 6 7 3 2 1 8 7-Methyl-bicyclo[4.2.0]octan-3-one
Some nomenclature If substituents are present, number the bridge ring system beginning at on bridge-head, proceeding first along the longest bridge to the other bridge-head. The shortest bridge is named last
Practice Aldol products from what?? H H CH 3 CH 3 H 3 C CH 2 H H 3 C H 3 C CH 3 H
Practice Exercises Disguised signatures!? show how the following compounds could be synthesized by a path that Includes an aldol or mixed aldol condensation, H H Don t let disguises fool you!
Make these starting with ethyl acetate or diethyl malonate and anything else H H
How far can you expand this web? C H? C NaBH 4 C Cl C NH R LiAlH 4 H 3 + C C CH 3 NH 2
Interconversions Problem: show reagents and experimental conditions to bring about each reaction 1 PhCH 2 CH 2 3 9 PhCH 2 CH 2 H PhCH 2 CCl 5 4 6 PhCH 2 CNH 2 7 PhCH 2 CCH 3 PhCH 2 CH 2 NH 8 2 10 11 PhCH 2 CH
Next. PLYMERS Jöns Jacob BerzeliusHermann Staudinger (1779-1848) (1881-1965) Wallace Hume Caroth (1896-1937)
Plastics!!!! The Graduate (1967): Recent college graduate Benjamin Braddock is trapped into an affair with Mrs. Robinson, who happens to be the wife of his father's business partner and then finds himself falling in love with her teenage daughter, Elaine. The Graduate