jo060598e_si_006.cif (20.81 kB)
Rearrangements of the Diels−Alder Cycloadducts Obtained from Acetylenic Sulfones and 1,3-Diphenylisobenzofuran
dataset
posted on 2006-07-07, 00:00 authored by Thomas G. Back, Masood Parvez, Huimin Zhai1,3-Diphenylisobenzofuran afforded Diels−Alder cycloadducts 4a,b with n-butyl- and phenyl-substituted
acetylenic sulfones 3a,b, respectively. The products underwent various types of rearrangements under
pyrolytic, acid-catalyzed, and photochemical conditions. In the presence of acid, or upon heating in xylenes,
they afforded the ketones 5a,b. In addition, the dehydration product 7a was produced from the pyrolysis
of 4a, and the unexpected transposed ketone 6b was generated under acid-catalyzed or pyrolytic conditions
from 4b via a postulated epoxide intermediate. The photolysis of 4a afforded ketone 5a as the sole
isolated product, whereas 5b afforded oxepin 8b and indenyl phenyl ketone 9b. The formation of the
latter two products can be rationalized by a series of pericyclic reactions. These include an intramolecular
[2+2] cycloaddition, followed by a 1,3-dipolar cycloreversion, for the transformation of 4b to 8b and a
series of electrocyclic and [1,3]sigmatropic reactions to convert 8b into 9b.