I just came across on something interesting on Reddit:
The reaction conditions are really mild, even through it's a photochemical reaction it does not require UV light, it simply goes with low energy red
light and a simple catalyst: methylene blue.
The reaction intermediate is a peroxide:
-here they used a high pressure mercury lamp what have emitted a lot UV, this method is reported at: Tetrahedron Letters No. 6. pp. 435 - 430,
1976 -french text!
After new year I will look up a few 2,3 disubstitued indole in the lab and try it out on a small scale, this rxn looks really promising for the
production of quinolones from indoles. And also could by tried out on other substances.
If this works, than there would be a safe, well working and easily made photochemical oxidation for everyone.
Any ideas?(:
For further reading the reaction is described at:
The Synthesis of Melohenine B and a Related Natural Product
Christopher S. Lancefield , Linna Zhou , Tomas Lébl , Alexandra M. Z. Slawin , and Nicholas J. Westwood
Org. Lett., 2012, 14 (24), pp 6166–6169
DOI: 10.1021/ol302859jDJF90 - 28-12-2012 at 21:34
Quote:
If this works, than there would be a safe, well working and easily made photochemical oxidation for everyone
So long as "everyone" can get benzoquinone (or make it), then the photodimerization to benzopinacol is safe, facile and high yielding. Clearly no good
for those of us in the UK where the sun rarely shines, but everyone else ought to be fine. Heres a prep: http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv2...
On the talk of photochemical reactions, I once did the radical addition of TsI to an alkyne. The light is meant to provide energy for homolysis of the
S-I bond, but it is so weak that the reaction would proceed in absolute darkness if left overnight. Obviously the tosyl iodide had to be made freshly
on the day the reaction was to be performed, because it went bad pretty quick. I didn't even bother trying to NMR it (OpenAccess machine = queue).
[Edited on 29-12-2012 by DJF90]smaerd - 29-12-2012 at 06:44
That is really neat reaction kristof. DJF90 thanks for sharing that now I have another series of experiments to do .
The scary part about photochemistry imo is the peroxides that can be/are formed. Often times papers leave out information about such side-products and
if a work-up isn't done with care, or the solvent is stripped without removal, well - BANG. I love the use of sensitizers especially affordable ones.
It seems like in a lot of modern total synthesis' that there is a photochemical, electrochemical, or even ultrasound step which completely changes the
reaction scheme. I feel like understanding these synthetic tools is of large importance. As for me I need to step up on the classic organic side of
things before diving into radical cascades hehehe.
edit - I also uploaded a small primer on photochemistry it lightly touches on sensitizers, solvent selection, etc.
"Organic Photochemistry", Prof. Dr. Burkhard König, Institut für Organische Chemie, Universität Regensburg
.