From Natural to Rationally Designed Artificial Enediynes: Towards New Anticancer Antibiotics Activable at Will - Polyynes: Synthesis, Properties, and Applications - page 474

SCHEME 19.33
the s-cis derivative. The main approach that has been followed is to gener-
ate the allene functionality from an opportunely functionalized alkyne
moiety, for example from a propargyl dicarboxylate 124 as illustrated in
Scheme 19.34. 116
SCHEME 19.34
In contrast to di-radicals such as 121 (Scheme 19.33), di-radicals origi-
nated by the Myers-Saito rearrangement are known to have an ionic
character in protic solvents and this nature is thought to reduce their DNA
damaging ability. However, it has been shown by Shibuya 117 that the pre-
sence of an electron withdrawing group in the benzylic position produces
a dehydrotoluene species with an enhanced diradical character.
19.5.4 P HOTOCHEMICAL C YCLOAROMATIZATION R EACTION
An alternative to thermal cycloaromatization is represented by photo-
activable enediyne systems, where a stable enediyne molecule is activated