REAPPRAISAL OF THE STEREOCHEMISTRY OF ELECTROPHILIC ADDITIONS TO 3-NORCARENES - X-RAY AND H-1-NMR ANALYSIS OF NORCARENE EPOXIDE CONFORMATION - ROLE OF MAGNETIC ANISOTROPIC CONTRIBUTIONS OF EPOXIDE RINGS

The stereochemical outcome of the addition of singlet oxygen, Br+, and peracid to four structurally varied 3-norcarenes has been investigated to obtain direct insight into prevailing product-determining steric effects in these systems. The various end products have been interconverted chemically to elucidate relative configuration. The stereochemical assignments have been established by reference to two 7, 7-dibromo epoxides, the structures of which were elucidated by three-dimensional X-ray methods. Approach of an electrophile anti to the cyclopropane ring was seen to be preferred in each of the cases examined, although the product ratios did vary with the particular substitution plan. The preferred conformations of the 3-norcarene epoxides have been assessed by 1H NMR spectroscopy through analysis of vicinal coupling constants. Finally, the question of epoxide ring anisotropy effects is addressed. © 1979, American Chemical Society. All rights reserved.