University:
Massachusetts Institute of Technology
Course:
5.37 | Introduction to Organic Synthesis Laboratory
Academic year:

2021
Views:

464

Pages:

4
Author:

Nomes67i

Massachusetts Institute of Technology Organic Chemistry 5.37 Lecture 2 Introduction to Organic Synthesis The Diels-Alder Reaction, Part II RE RZ RE EWG RZ R1 R'Z R2 R'E R'Z EWG + R2 R1 R'E Our results will play a role not only in the discussion of theoretically interesting questions . . . . but probably also will yield greater significance in a practical sense. Thus it appears to us that the possibility of synthesis of complex compounds related to or identical with natural products such as terpenes, sesquiterpenes, perhaps also alkaloids, has been moved to the near prospect. . . . . . We explicitly reserve for ourselves the application of the reaction discovered by us to the solution of such problems. Otto Diels Otto Diels and Kurt Alder Justus Liebigs Annalen der Chemie 460, 98 (1928) Kurt Alder For Additional Reading . . . . (1) “Advanced Organic Chemistry, Part A: Structure and Mechanisms”, Fifth Edition, by F. A. Carey and R. J. Sundberg, Springer, 2007, Chapter 10 (“Concerted Pericyclic Reactions”), pp 833-873. (2) “Advanced Organic Chemistry, Part B: Reactions and Synthesis”, Fifth Edition, by F. A. Carey and R. J. Sundberg, Springer, 2007, Chapter 6 (“Concerted Cycloadditions, Unimolecular Rearrangements, and Thermal Eliminations”), pp 473-526. (3) “Organic Chemistry” by J. Clayden, N. Greeves, S. Warren, and P. Wothers, Oxford University Press, 2001, Chapter 35 (“Pericyclic Reactions I: Cycloadditions”), pp 905-924 and Chapter 45 (“Asymmetric Synthesis”), pp 1219-1232. Regiochemical Course of the Diels-Alder Reaction: The "Ortho-Para Rule" R R R EWG EWG + not "ortho" EWG EWG not + R R R EWG "meta" EWG "meta" "para" Stereochemical Course of the Diels-Alder Reaction Intrinsic Stereoselectivity  Suprafacial with respect to the diene  Suprafacial with respect to the dienophile  Alder endo rule Asymmetric Induction  Substrate control by chiral dienophiles  Substrate control by chiral dienes  Stereocontrol via chiral auxiliaries Catalytic Asymmetric Cycloadditions Stereochemical Course of the Diels-Alder Reaction: Suprafacial with respect to the diene component R R E H H EWG H E EWG R R R H EWG H EWG H R EWG EWG H EWG cis R H H Z EWG R EWG R EWG H R E R H EWG EWG R H trans Stereochemical Course of the Diels-Alder Reaction: Suprafacial with respect to the Dienophile Component EWG EWG EWG H H RZ H RE RZ RE RZ RE Stereochemical Course of the Diels-Alder Reaction: The Alder Endo Rule RE RE RE RZ RZ EWG RZ EWG EWG H RE RE RZ H H EWG RE RZ Exo Addition RZ H H H The term "endo" originates in the terminology used to describe the stereochemistry of substituents on bicyclic ring systems. A substituent is said to be endo when it is trans to the smaller of the two bridges; an exo substituent is cis to the smaller bridge. EWG EWG this bridge has 1 carbon REXO this bridge has 2 carbons H O H RENDO O O O H O O O This is an endo Diels-Alder adduct H This is an exo Diels-Alder adduct Steric vs. Stereoelectronic Effects in Determining Endo Selectivity + CHO CHO major CH3 CH3 minor CHO

Introduction to Organic Synthesis: The Diels-Alder Reaction, Part II

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