sentences:  The major product forms from attack at the 1 position, due to the instability of the twist boat product formed by addition at the 2 position (disfavored by approximately 5 kcal/mol).Similarly, the Fürst-Plattner rule applies to nucleophilic additions to imines and halonium ions.A recent example of the Fürst-Plattner rule can be seen from "Chrisman" et al.