When 1,2,3-selenadiazoles synthesized from cyclic ketones were treated with
an excess amount of olefins at 130 degrees C, the addition of a vinyl radi
cal, which was generated in situ by the denitrogenation of 1,2,3-selenadiaz
oles, to a carbon-carbon double bond followed by intramolecular cyclization
proceeded efficiently giving the corresponding dihydroselenophenenes in mo
derate to good yields along with the formation of the corresponding 1,4-dis
elenins and selenophenes as by-products. In this reaction, the number of ca
rbon atoms on the cyclic ring of the ketones used as the starting materials
in the synthesis of the 1,2,3-selenadiazoles plays an important role in th
e selectivity of the products. In contrast to the reaction of the 1,2,3-sel
enadiazoles prepared from the cyclic ketones, in the reaction of 1,2,3-sele
nadiazoles derived from aromatic and linear ketones, the dihydroselenophene
ne and 1,4-diselenins derivatives were not obtained and the corresponding a
lkynes were formed as the sole product. (C) 2000 Published by Elsevier Scie
nce S.A. All rights reserved.