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Studies on the benzoxazine series. Part 3—Preparation and 13C NMR structural Study of γ Effects of Some N-substituted 3,4-dihydro-2H-1,3-benzoxazines

✍ Scribed by Kari Neuvonen; Kalevi Pihlaja

Publisher
John Wiley and Sons
Year
1990
Tongue
English
Weight
623 KB
Volume
28
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

Seventeen N‐substituted 3,4‐dihydro‐2__H__‐1,3‐benzoxazines [N‐substituent = Et, Pr^i^, Bu^t^, CH~2~C~6~H~5~ or CH(CH~3~)C~6~H~5~] were prepared and their structures studied in the light of ^13^C chemical shifts. The γ effects caused by C(α)‐methyl or C(α)‐phenyl substitution at the heterocyclic ring carbons were found to be valuable structural parameters. By using N‐tert‐butyl derivatives as models, and by dividing γ~tot~ effects into their components, the rotamer populations due to the rotation around the NC(α) bond could be evaluated. The method also allows the configurational assignment of diastereomeric N‐α‐methylbenzyl derivatives. The effect of the half‐chair structure on the ^13^C NMR parameters is discussed.

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