And for bonus fun, positioning a diene and a dienophile at opposite ends of a macrocycle leads to a transannular Diels-Alder, which has the awesome acronym TADA! A tethered diene and dienophile will form a fused bicycle (and tether a dienophile to a cyclic diene to make a sweet looking tricycle). An ambitious professor will make the diene a cyclic diene, which yields a bridged bicyclic system. For most undergraduate courses, the regiochemical implications of this are enough. Your prototypical, run-of-the-mill Diels-Alder reaction yields a cyclohexene. This is one of the few times where thoroughly wading through the theory behind the reactions pays great dividends in clarifying the reactions and predicting their products. Pericyclic reactions are an immensely rewarding cadre of reactions to study. Like Kekulé’s apocryphal tail-eating snake, the electrons travel around in a ring in this mechanism the Diels-Alder reaction joins other privileged mechanisms – electrocyclizations ( Nazarov) and sigmatropic rearrangements ( Cope, Claisen) – in the tribe known as pericyclic reactions. Note that the electrons don’t really start and end anywhere in particular. And, like CJ, I also went with the hand-drawn structures.)īut the story is so much more interesting and rich. And that may be as deep as most undergraduate texts delve into the Diels-Alder reaction. Straightforward, right? The Diels-Alder is usually the only cycloaddition reaction to make it into undergraduate organic textbooks. This is the bare-bones Diels-Alder reaction we all remember from undergraduate organic chemistry classes. Striped away from all its layers of complexity, at its core, the Diels-Alder reaction (here’s a 3-D animation of the Diels-Alder Reaction) is a reaction of a conjugated diene (4π electrons, in the s-cis conformation) and an alkene (2π electrons, called the dienophile) to form a cyclohexene ring – the reaction is classified as a cycloaddition. Oh, by the way, the pair won the 1950 Nobel Prize in Chemistry for the reaction. They write in their 1928 paper: “he possibility of synthesis of complex compounds related to or identical with natural products such as terpenes, sesquiterpenes, perhaps even alkaloids, has been moved to the near prospect … We explicitly reserve for ourselves the application of the reaction developed by us to the solution of such problems.” Fortunately for us, this exclusivity no longer applies.

And I am grateful to BRSM for deciding not to blog about the Diels-Alder Reaction.įirst reported in 1928 by Otto Diels (1876-1952) and his graduate student Kurt Alder (1902-1958), the chemists at once saw the importance of their work and wanted the exclusive rights to utilize their reaction. It is by far my favorite reaction and the subject of my Blog Carnival Post. Straightforward enough for an undergraduate organic chemistry class, yet intricate enough to spend several days in a graduate organic chemistry class reading into the engrossing story that is the Diels-Alder reaction. It appears deceptively simple and yet has the ability to create immense structural complexity often without additional reagents and sometimes solvent-free. No reaction is more elegant, more heartwarmingly satisfying than the Diels-Alder reaction. This post was excerpted and featured in a recent edition of C&ENews

Homo lumo diels alder