Effect of Sulfonyl Protecting Groups on the Neighboring Group Participation Ability of Sulfonamido Nitrogen

The addition of elemental bromine dissolved in CH2Cl2 to para-disubstituted benzodiazocines where X is the same (H, CH3, Br, OMe, NO2) or a different substituent as X and Y (CH3, Br; OMe, NO2) has been found to proceed in most cases with competition between two pathways. While conventional trans-1,2-addition operates predominantly, electron-releasing groups also foster a ring-contraction process with ultimate 1,3-positioning of the pair of bromine atoms. The observed regio- and stereoselectivities, confirmed where necessary by X-ray crystallographic analysis, establish the capability of sulfonamide nitrogen centers to engage in neighboring group participation.