Download presentation

Presentation is loading. Please wait.

Published byArjun Southerly Modified over 3 years ago

1
Stereoelectronic requirement for Ei-type Elimination: abstraction of H–atom by leaving group "Cope–elimination" "Chugaev Elimination" “near coplanarity" “near coplanarity"

2
Regioselective Cope-Elimination "Sulfoxide (Selenoxide)–elimination" “Enone Synthesis" “near coplanarity"

3
opportunity Synthesis of -methylene- -lactone trans cis

4
“Peterson Olefination"

5
“Nozaki-Yamamoto Elimination for Regio- and Stereo-defined Allylic Alcohol Synthesis from Epoxides" acis-base hybrid reagent (A-B reagent)

6
Stereoelectronic Requirements: SUMMARY sp 3, sp 2, and sp Reaction Centers Attacked by X – Stereoelectronic Requirements: SUMMARY sp 3, sp 2, and sp Reaction Centers Attacked by X – sp 3 sp 3 sp 2 sp 2 sp sp Epoxides and related Epoxides and related endo exo X should be second periodical elements

7
Stereoelectronic Control in Nature: Polyene–Epoxide Cyclization squalene squalene epoxide lanosterol cholesterol H+H+

8
Biomimetic Polyene–Alcohol Cyclization: Strategy for Stereoselective Steroid Synthesis: W. S. Johnson H+H+ HOH progesterone Ozone KOH Biomimetic Synthesis: learning from nature

9
Baldwin Rule exo-cyclization endo-cyclization The First Rule:a) 3~7-Exo–Tet Cyclization : favored b) 5~6-Endo–Tet Cyclization : disfavored (a)(b) "3–Exo–Tet" "5–Endo–Tet"

10
The Second Rule: a) 3~7-Exo–Trig Cyclization : favored b) 3~5-Endo–Trig Cyclization : disfavored 6~7-Endo–Trig Cyclization : favored (a) (b)

11
The Third Rule:a) 3~4–Exo–Dig Cyclization : disfavored 5~7–Exo–Dig Cyclization : favored b) 3~7–Endo–Dig Cyclization : favored (a) (b)

12
The Fourth Rule: (Enol...)-Exo-Tet (a) 3~7–(Enolexo)–Exo–Tet: favored (b) 3~5–(Enolendo)–Exo–Tet: disfavored (c) 6~7–(Enolendo)–Exo–Tet: favored (Enolexo)–Exo–Tet The Fifth Rule: (Enol...)-Exo-Trig (a) 3~7–(Enolexo)–Exo–Trig: favored (b) 3~5–(Enolendo)–Exo–Trig: disfavored (c) 6~7–(Enolendo )–Exo–Trig: favored (Enolendo)–Exo–Trig 1(a) 5–Exo–Tet: favored4(b) 5–(Enolendo)–Exo–Tet: disfavored enolate O-alkylation (S N 2)C-alkylation (S N 2)addition

13
5–(Enolexo)–Exo–Tet 7–(Enolendo)–Exo–Tet The Fourth Rule (a): favored The Fourth Rule (a): favored The Fourth Rule (c): favored The Fourth Rule (c): favored

14
6–(Enolendo)–Exo–Tet 6–Exo–Tet much faster > The Fourth Rule (c): favored The Fourth Rule (c): favored The First Rule (a): favored The First Rule (a): favored not produced

15
Aryne or Benzyne (Dehydrobenzene) Aryne or Benzyne (Dehydrobenzene) Isolated Carbon-Carbon Multiple Bonds: # very low reactivity toward n-base (very low electrophilicity) # very low nucleophilicity of n-base toward carbon-carbon multiple bonds except for arynes H+H+

16
Evidence in support of non-S N Ar mechanism cine substitution S N Ar Mechamism

17
Preparation of Arynes: Break Through B – slow elimi. fast B – slow excess B - drawback Break Through: K. Suzuki, 1991 BuLi v. fast elimi. fast + 90% [4 + 2] cycloaddition halogen/metal exchange: very fast

18
n-BuLi THF, –78 ℃ <10 min electron withdrawing inductive effect R = Me: 76% R=Bn: 82% K. Suzuki, JACS,1992: Total Synthesis of (+)-Gilvocarcin M Tf 2 O/DIPEA CH 2 Cl 2 99%

19
(+)-Gilvocarcin M

Similar presentations

Presentation is loading. Please wait....

OK

Aromatic Substitution Reactions

Aromatic Substitution Reactions

© 2018 SlidePlayer.com Inc.

All rights reserved.

To ensure the functioning of the site, we use **cookies**. We share information about your activities on the site with our partners and Google partners: social networks and companies engaged in advertising and web analytics. For more information, see the Privacy Policy and Google Privacy & Terms.
Your consent to our cookies if you continue to use this website.

Ads by Google

Ppt on phonetic transcription exercises Ppt on autonomous car Full ppt on electron beam machining process Ppt on introduction to object-oriented programming with c++ Download ppt on electric current and circuits Economics ppt on lpg Ppt on body language in communication Ppt on magic of thinking big Ppt on image compression using wavelet transform Ppt on digital photography