The solution conformation of N-methyl-2-(tributylstannyl)piperidines has been determined through the use of vicinal 119Sn-13C coupling constants, revealing a conformational distortion caused by an unexpected stereoelectronic effect in some cases. Specifically, the "equatorial" conformer is distorted into a half-chair, in which the nitrogen lone pair eclipses the C-Sn bond. This distortion, which "costs" approximately 1 kcal/mol, correlates with a conformational dependence of geminal 119Sn-15N couplings and a possible correlation with reactivity in the tin-lithium exchange reaction.
N-Methyl trans-fused perhydroisoindolines substituted with a tributylstannyl group in the 2-position have been prepared and used as precursors of the corresponding alpha-aminoorganolithiums. The steric course of the reactions of these and other conformationally rigid organolithiums with various electrophiles is summarized and compared with the steric course of the unsubstituted analogs. A mechanistic rationale for the steric course of electrophilic substitutions of these organolithiums is discussed. Pathways involving both polar electrophilic substitutions and radical couplings were observed with different electrophiles.
The ultraviolet and near-visible light absorption of a nuniber of substituted trar~s-chalco~les are reported.Chalcones (I) possess a conlplex conjugate system since the carbony1 group is interposed between phenyl and styryl groups. trans-Chalcones generally show two main regions of selective ultraviolet absorption, one near 230 n~p (band 11), the other beyond 300 inp (band I) (see Table I). These two nlaxima were formerly attributed (1) to the partial benzoyl (PhCO-) and cinna~noyl (PhCI-I=CI-ICO-) chroinophores, respectively, but the long wavelength band (band I) is now believed to involve the whole conjugate system (2). A third band, a t 205 mp, has been observed (3) and may be attributed to a modified E-band of the phenyl groups (cf. benzene A, , , 205 mp, E 6 300 (4)).
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