Halonium ions bicyclic

Moreover, the cyclization of the azetidinonc 11a, performed with AT-bromosuccinimide in acetonitrile, afforded the bicyclic product 13a only in quantitative yield, which is an intermediate in the synthesis of carbapenems. Under the same reaction conditions, lib afforded 13b in quantitative yield. The stereochemistry of both 13a and 13b was assigned either by NOE experiments or X-ray crystallographic analysis. The reaction proceeds via the intermediate /V-brominated compound 12. Bromine then migrates to the double bond and the amidic nitrogen attacks the formed halonium ion to give 13237. 

Dialkylhalonium fluoroantimonate salts can be isolated as crystalline salts and are versatile, very reactive alkylating agents. As the differing halogen atoms effect a range of selectivity, they were found to be more versatile than trialkyloxonium salts. Several bicyclic halonium ions also have been prepared and studied151. ... 

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