ISSN:
0009-2940
Keywords:
[5]Helicenes, methano-bridged
;
Aromatic hydrocarbons, polycyclic
;
Cycloheptatriene, all-benzoanellated, flexibility of
;
Distorted aromatic rings
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Intramolecular Friedel-Crafts alkylation of 1-(hydroxymethyl)[5]helicenes 1-R and 15-Me leads to 10,11-methano-bridged dibenzo[c,g]phenanthrenes 2-R and 16-Me, respectively. These molecules are shaped like the back of a turtle as shown by X-ray crystal structure analysis. Their nonplanarity, however, is not rigid, as revealed by the temperature dependence of their 1H-NMR spectra. With inversion barriers of about 62.4 and 67.1 kJ mol-1 2-H and 2-Me are surprisingly flexible. A remarkable diastereoselectivity is observed in the addition of methyl- and phenylmagnesium bromide to 1-formyl[5]helicenes 14-Me leading to secondary alcohols 15a, b-Me, which cyclize to bridged hydrocarbons 16a, b-Me, in which the substituents R=Me, Ph are in the thermodynamically less favorable endo-position. Upon heating, endo-16a,b-Me isomerize to exo-6a, b-Me irreversibly.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19931260722
