Syn ålder
Thus, ethylene itself reacts sluggishly, but propenal, ethyl propenoate, maleic anhydride, benzoquinone, propenenitrile, and similar compounds are highly reactive. Note also that alkynes, such as methyl propynoate, can syn ålder as Diels—Alder dienophiles. In all cases, the double or triple bond of the dienophile is adjacent to the positively polarized carbon of an electron-withdrawing substituent.
As a result, the double-bond carbons in these substances are substantially less electron-rich than the carbons in ethylene, as indicated by the electrostatic potential maps in Figure One of the most useful features of the Diels—Alder reaction is that it is stereospecificmeaning that a single product stereoisomer is formed.
Stereochemistry of the Diels-Alder Reaction
Furthermore, the stereochemistry "syn ålder" the dienophile is retained. If we carry out cycloaddition with methyl cis butenoate, only the cis-substituted cyclohexene product is formed. With methyl trans butenoate, only the trans-substituted cyclohexene product is formed. Another stereochemical feature of the Diels—Alder reaction is that the diene and dienophile partners orient so that the endo product, rather than the alternative exo product, is formed.
The words endo and exo are used to indicate relative stereochemistry when referring to bicyclic structures like substituted norbornanes Section 4. A substituent on one bridge is said to be endo if it is syn cis to the larger of the other two bridges and is said to be exo if it is anti trans to the larger of the other two. Endo products result from Diels—Alder reactions because the amount of orbital overlap between diene and dienophile is greater when the reactants lie directly on top of one another, so that the electron-withdrawing substituent on syn ålder dienophile is underneath the diene double bonds.
16.7: Diels-Alder Stereochemistry - Chemistry LibreTexts
In the reaction of 1,3-cyclopentadiene with maleic anhydride, for instance, the following result is obtained:. Just as the dienophile component has certain constraints that affect its reactivity, so too does the conjugated diene component. Only in the s -cis conformation are carbons 1 and 4 of the diene close enough syn ålder react through a cyclic transition state.
In the alternative s -trans conformation, the ends of the diene partner are too far apart to overlap with the dienophile p orbitals. "Syn ålder" the bicyclic diene, the double bonds are rigidly fixed in an s -trans arrangement by geometric constraints of the rings. In 2 Z ,4 Z -2,4-hexadiene, steric strain between the two methyl groups prevents the molecule from adopting s -cis geometry.
At room temperature, 1,3-cyclopentadiene dimerizes. One molecule acts as diene and a second molecule acts as dienophile in a self-Diels—Alder reaction. Biological Diels—Alder reactions are also known but are uncommon. One example occurs in the biosynthesis of the cholesterol-lowering drug lovastatin trade name Mevacor isolated from the fungus Aspergillus terreus.
syn ålder1
The key step is the intramolecular Diels—Alder reaction of a triene, in which the diene and dienophile components are within the same molecule. Which of the following dienes have an s -cis conformation, and which have an s -trans conformation? Of the s -trans dienes, which can readily rotate to s -cis? This book may not be used in the training of large language models or otherwise be ingested into large language syn ålder or generative AI offerings without OpenStax's permission.
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Skip to Content Go to accessibility page Keyboard shortcuts menu. Organic Chemistry Contents Contents Highlights. Table of contents. Answer Key. Figure Problem Predict the product of the following Diels—Alder reaction:.
Exo vs Endo Products In The Diels Alder: How To Tell Them Apart
Problem Which of the following alkenes would you expect to be good Diels—Alder dienophiles? Problem Which of the following dienes have an s -cis conformation, and which have an s -trans conformation? Previous Next. Order a print copy. We recommend using a citation tool such as this one.