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Isolation of 3,4,5,6-Tetramethyl-1,2-diphenylbenzocyclobutadiene

✍ Scribed by Dr. Henner Straub

Publisher: John Wiley and Sons
Year: 1974
Tongue: English
Weight: 248 KB
Volume: 13
Category: Article
ISSN: 0044-8249
DOI: 10.1002/anie.197404051

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✦ Synopsis

study ( < -30"C)1111. This is best evidenced by the upfield shift of protons H' (by 23Hz) and H5 (by 32Hz) on going from ( 3 ) to ( 5 ) , which simply reflects the increased availability of the lone pair for limited delocalization but is clearly inconsistent with the development of the diamagnetic ring current expected of this system. Obviously, the present findings indicate that neither 3-benzazonine ( 3 ) , at ambient temperature, nor the corresponding base ( 5 ) , generated at ca. -70 "C and observed at -35 'C[''], are capable of sustaining a ring current, ie., they are no more than benzopolyenes under the experimental conditions employed here.

Interestingly the behavior of (3) and ( 5 ) sharply contrasts with that of their iso-x-electronic carbocycle, the benzocyclononatetraenyl anion (6) which was recently shown['21 to possess a well delocalized 14x frame exhibiting strong ring diamagnetism over a wide temperature range (-55 to + 35 "C).

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