In the selective α-cleavage cycloaddition of oxiranes with heterocumulenes catalyzed by tetraphenylstibonium iodide, the direction of oxirane fission at first stage is not significant, while the difference of reaction behaviors of two antimony alkoxide intermediates (Ph 4 SbOCH 2 CH (R 1) I and Ph 4 SbOCH (R 1) CH 2 I), insertion of heterocumulenes and cyclization to original oxiranes, is responsible for the unusual selectivity.
