5-Endo-trigonal reactions: a disfavoured ring closure

A number of polyfunctional molecules have been examined as substrates for the 5-Endo-Trigonal ring-forming reaction, and it has been found that for first-row elements this is a disfavoured process, alternative reactions of type 5-Exo-Trig generally taking precedence; one case of a 5-Endo-Trig closure for a second-row element, sulphur, has been found.