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[摘要]：Several typical 13C-NMR displacements (of C=O, C(a), C(beta), and C(ipso)), as well as conformational or energy properties (S-N-C=O dihedral angle, Delta E syn/anti; HOMO/LUMO) could be correlated with the electronic parameters of p-substituted N-cinnamoylbornane-10,2-sultams 2. Even under nonchelating conditions, the pyramidalization of the sultam N-atom decreases for electron-attracting p-substituents, inducing a modification of the sultam-ring puckering. Detailed comparison of the X-ray structure analyses of 2b, 2d, and 2m showed that the orientation of the sterically directing pseudo-axial S=O(2) and H-C(2) is modified and precludes any conclusion about the p-facial stereoelectronic influence of the N lone pair on the alkyl Grignard 1,4-addition. We also showed that the aggregating alkyl Grignard reagent may be used in equimolar fashion, demonstrating that the sultam moiety is chelated with a Lewis acid such as MgBr2. The Schlenk equilibrium may also be used to generate the appropriate conditions of effective 1,4-diastereoselectivity. Although the anti-s-cis/syn-s-cis difference of conformational energies for N-cinnamoyl derivatives 2 is higher than for the simple N-crotonoyl analogue, an X-ray structure analysis of the SO2/C=O syn derivative 10 confirms the predictive validity of our conformational calculations for Delta E=1.8 kcal/mol. |
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