Abstract
The singlet cyclization of
Z
(or
E
)-1-biphenyl-2-yl-1-phenylpropene proceeds stereoselectively to
cis
(or
trans
)-9-phenyl-10-methyl-9,10-dihydrophenanthrene (the
cis
-isomer has been characterized by
X
-ray crystallography) while the triplet cyclization gives a [
trans
]/[
cis
] ratio of 9 : 1 whatever the starting isomer.