ABSOLUTE ASYMMETRIC SYNTHESIS. I. ON THE MECHANISM OF THEPHOTOCHEMICAL ABSOLUTE ASYMMETRIC SYNTHESIS OF HELICENES WITH CIRCULARLYPOLARIZED LIGHT. . WAVELENGTH DEPENDENCE OF THE OPTICAL YIELD OFOCTAHELICENE. Page: 3 of 17
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Numerous attempts have boon made to induce asymmetric synthesis in
hotochmical reactions by employing circularly polarized lghL.
Until recently, however, the rotations found were marginal, anl i ne
case was the source of the rotation positively identified. Furthrmor.,
in only one experiment were opposing rotations found with right arnd
left circularly polarized light (RCL and LCL), and in this case the
optical activity disappeared upon prolonged irradiation. All recent
attempts to reproduce many of these results have failed.5
After the work reported here was completed, Mradpour et al.
reported that irradiation of compounds Ia and -lb leads to nonracemic
yields of hexahelicene.
We wish to report irradiations of the ,2-diarylethylenes (I-IV in
the presence of iodine to the helicenes VI-IX with LCL and RCL.7-1
All resulted in the formation of an unequal mixture of enantiomers of
the respective helicenes (Scheme 1)
Results and Discussion
With each of the substrates I-I, twe samples were irradiated under
identical conditions with RCL and LCL, and except for the marginal
optical activity reported for irradiation of Ia, significant optical
activity was observed.
Equal and opposite rotations were obtained in the products resulting
from irradiation with RCL and LCL, and the compounds responsible for the
optical activity were identified by chromatography and by the characteristic
snape of the induced RD and CD curves as the expected helicenes (T'Ibe I) .
In each case it was found that irradiation with LCL led to a positive
rotation, whereas irradiation with RCL led to a negative rotation.
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Bernstein, William J.; Calvin, Melvin & Buchardt, Ole. ABSOLUTE ASYMMETRIC SYNTHESIS. I. ON THE MECHANISM OF THEPHOTOCHEMICAL ABSOLUTE ASYMMETRIC SYNTHESIS OF HELICENES WITH CIRCULARLYPOLARIZED LIGHT. . WAVELENGTH DEPENDENCE OF THE OPTICAL YIELD OFOCTAHELICENE., article, May 1, 1971; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc894330/m1/3/: accessed February 16, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.