Comments on: Exo vs Endo Products In The Diels Alder: How To Tell Them Apart

By: James Ashenhurst

James Ashenhurst — Wed, 15 Feb 2023 02:36:58 +0000

In reply to Amrendra Kumar. Try it for yourself. What do you think?

By: Amrendra Kumar

Amrendra Kumar — Mon, 13 Feb 2023 18:10:12 +0000

Really its a nice post & have great topic discussion .
its a concept booster…..
thankyou so much!
actually my query regarding this topic is that:

when cis,cis-3,4-dimethylcylobutene is subject to reaction photochemically dis-rotation ring opening, what will be the product?
either cis or trans ?

By: James Ashenhurst

James Ashenhurst — Wed, 15 Jun 2022 19:00:44 +0000

In reply to Mike W. There's been some previous discussion on this thread regarding IUPAC and their use of exo/endo versus how the terms are actually used in practice. My general opinion on this one is that IUPAC can get stuffed because nobody follows their recommendations on this topic. If there is a specific image that is causing confusion to you, could you specify which one (image filenames are numbered, so that would help).

By: Mike W

Mike W — Sun, 12 Jun 2022 20:38:03 +0000

This is the IUPAC definition of endo/exo/syn/anti in bicyclo alkane systems: https://goldbook.iupac.org/terms/view/E02094

The names under the two structures seem to contradict the definition above. Is this an error?

Mike

By: James Ashenhurst

James Ashenhurst — Tue, 10 Mar 2020 02:26:27 +0000

In reply to eric. Thank you Eric. Glad you found it helpful

By: eric

eric — Tue, 10 Mar 2020 00:27:54 +0000

this is incredibly well done.
i finally understand the endo rule

By: Dr. Kamaljit Singh

Dr. Kamaljit Singh — Mon, 17 Feb 2020 06:24:14 +0000

How do we depict formation of endo and exo products in cycloaddition reactions involving 1,3-dipolarophile such as a nitrone and a dipolariphile such as an activated olefin. Thanks

By: James Ashenhurst

James Ashenhurst — Tue, 11 Feb 2020 20:43:12 +0000

No worries! I always teach that the enantiomer has the opposite R,S designation so this exception is a very useful thing to keep in mind!!!

By: DeltaG

DeltaG — Tue, 11 Feb 2020 20:40:53 +0000

you are right. it was my fault for relying on ChemDraw to name these. should have relied on the old school do-it-by-hand.

By: James Ashenhurst

James Ashenhurst — Fri, 07 Feb 2020 04:35:52 +0000

In reply to DeltaG.

If we started with dimethyl(1R, 2R, 3R, 4S)-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate and did a single swap (i.e. flipped) all four stereocenters, you would get the enantiomer. Agree?
If so, then would you agree that the name of that enantiomer would be (1S, 2S,3S,4R)bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate?
As it turns out this is not correct (!!) due to a quirk of IUPAC nomenclature (priority of numbering). A picture says more than a lot of words would. Here is a link to an explanation I made. https://www.masterorganicchemistry.com/wp-content/uploads/2020/02/Supp-More-Iupac-exo-endo.gif

Here is a screenshot of the IUPAC rule from the Blue book: https://www.masterorganicchemistry.com/wp-content/uploads/2020/02/Supp-priority-of-R-over-S-1.png