New structurally interesting cyclopropane derivatives. A world of wonders and surprises
A. de Meijere1**, S. I. Kozhushkov1,
A. A. Fokin2, I. Emme1,
S. Redlich1, and P. R. Schreiner2
1Institut für Organische Chemie der
Georg-August-Universtität Göttingen,
Tammannstrasse 2,D-37077 Göttingen, Germany; 2Institut
für Organische Chemie, Justus-Liebig-Universität Giessen,
Heinrich-Buff-Ring 58, D-35392 Giessen, Germany
Abstract: The structurally intriguing [4]- and [5]triangulanes
have been prepared in enantiomerically pure form. Their surprisingly
high specific rotations are well reproduced by DFT/SCI computations
and stem from the fact that these hydrocarbons essentially are s-helicenes
(i.e., rigidly held helical arrangements of s-bonds).
Some light is shed on the properties of radical cations derived from
[3]- and [4]rotanes. While the former adopts Cs or C2v
symmetry, the latter retains the D4h symmetry of the neutral
hydrocarbon, according to highlevel computations. Experimental and computational
evidence is also presented that the antiaromatic cyclopentadienyl cation
is stabilized as a singlet ground state by five cyclopropyl substituents.
Yet, the three cyclopropyl groups in tricyclopropylamine do not favor
the formation of its radical cation, because they are not in the proper
orientation. When this amine radical cation is generated by cobalt g-irradiation
in a Freon matrix, evidence for a significant conformational change
is obtained by EPR spectroscopy. Finally, the conformational dynamics
of the newly prepared crowded molecules tetracyclopropyl- and tetraisopropylmethane
are discussed.
*Plenary lectures presented at the 16th International
Conference on Physical Organic Chemistry (ICPOC-16): Structure and Mechanism
in Organic Chemistry,San Diego, California, USA, 4�9 August 2002. Other
presentations are published in this issue, pp.
541�630.
**Corresponding author
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