Wednesday, January 14, 2009

bringing back the old school

I remember when I first started my PhD it was pretty common for the people in the group to use flash cards to learn and practice name reactions. In fact they flew around with such ubiquity that incoming postdocs would typically have to learn or re-learn a whole slew of them.

I would ask people for name reactions to study and add the suggestions to the pile of cards. One day while doing this the postdoc I was talking to harumphed when I got to the Ramberg-Bäcklund reaction. He commented that I shouldn't put less useful reactions in my cards, as they just take up space.

Ever since then I get sort of tickled when I see the Ramberg-Bäcklund in a new synthesis. I'll admit it's not very common, and by today's standards, really not too useful, but when it is used properly it is still pretty neat. So today, while piling through yet another day of ASAPs I ran into this:



The conversion of 27 to 5 is actually pretty sweet, and involves, of course, a Ramberg-Bäcklund.

No paper is without it's flaws, such as the implied enantiopurity of racemic 36, but the appropriate use of the classics is always welcome.

Also if anyone needs a named reactions book, get Bert's. It's totally sweet, chock full of a shitload of reactions, and really cheap (<$30 on 1-14-09 for the 2800 page pdf).

4 comments:

Dr. Miller said...

The authors get a 5:1 E:Z ratio in the R-B reaction. I am having a problem seeing how this reaction is that E/Z selective. Any ideas?

scientist 1 said...

This is not really a forum for discussion so much as a forum for making fun of people, but I'll comment.

The R-B is is general not known for selectivity, and this is mentioned in the review referenced in the paper (Chem. Comm., 1999, 217–227). It would appear that this example is under substrate control. The formation of the epi-sulfone prior to the chelotropic elimination should be the stereodefining step, and all previous ones should have at least some level of reversibility and/or facility of diastereomer equilibration. The 4 transition states (of 8 possible) leading to
the epi-sulfones, that in turn lead to the dominant product, must be most favorable, either individually or in concert.

That or your mom.

Dr. Miller said...

A very long winded of saying that you have no idea.

scientist 1 said...

No, I also referenced your mother.

Besides, I'm essentially correct, and I bet the authors had no idea which would be formed either except for the one geometry is present in the natural products implying it's favorable.