Tautomerization-mediated molecular switching between six- and seven-membered rings stabilized by hydrogen bonding.
1,3,4,6-Tetraketones typically undergo keto-enol tautomerism forming bis-enols stabilized by intramolecular hydrogen bonding in two six-membered rings. However, 1,3,4,6-tetraketones derived from the terpene ketone camphor and norcamphor exist as isomers with two distinguishable modes of intramolecular hydrogen bonding, namely, the formation of six- or seven-membered rings. The structural requirements for this so far unknown behavior were investigated in detail by synthesis and comparison of structural analogues. Both isomers of such 1,3,4,6-tetraketones were fully characterized in solution and in the solid state. Intriguingly, they slowly interconvert in solution by means of tautomerism-rotation cascades, as was corroborated by DFT calculations. The influence of temperature and complexation with the transition metals Pd, Rh, and Ir on the interconversion process was investigated.
Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg (Germany).
Golo
G
Storch
Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg (Germany).
Markus J
MJ
Spallek
Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg (Germany).
Frank
F
Rominger
Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg (Germany). trapp@oci.uni-heidelberg.de.
Oliver
O
Trapp
chelates; hydrogen bonds; ketones; molecular switches; tautomerism