PMR and CMR Spectra of Phthalideisoquinolines Conformational Analysis

The CD and ORD curves of phthalideisoquinolines have been recorded and interpreted.  

The erythro-nor base 10 exists mostly in conformation 10a. The 2 -H and S -CHaO signals are relatively upheld at 85.84 and 83.62, respectively, due to ring A shielding. In the erythro base 12, on the other hand, the 8-H signal appears upheld at 86.20 because of shielding by ring D, and conformation 12a prevails.  

The chemical shift of H-8 can also be used as a probe in determining conformation in the threo-nor and threo series. This signal is relatively upheld, at S6.32, in the case of the threo base 11 because of shielding by the lactone carbonyl in the favored conformation 11a. It is further downheld at 86.52 in the threo-nov base 9 since no shielding is involved in this instance, and conformation 9a is paramount.  

The CMR spectral assignments shown below have been made for j8-hydra-stine, a-hydrastine, corlumine, and adlumine. Chemical shifts at C-3 and C-4 were found to be diagnostic of the relative stereochemistry at C-1 and C-9.  

Irradiation of tetrahydrofuran solutions of (—)-a-narcotine and of (—)-j8-hydrastine resulted in epimerization at C-1 and C-9, so that racemic mixtures of diastereomers were obtained in each case.  

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