Bond Switch via Sulfuranes (10-S-3) and Formation of Novel Sulfuranes (10-S-4)

Abstract

Three types of the typical reaction and character of hypervalent sulfuranes are described mainly based on the results of the author's research group. First, it is presented that several types of iminothiadiazolines behaved as masked 1, 3-dipoles to react with activated acetylenes and imidates (nitriles) in the fashion of addition-elimination and addition-ring-transformation respectively, where the corresponding thiathiophthene analogous sulfuranes (10-S-3)were invoked as the intermediates. Second, ring-transformation (bond switch) equilibrations were observed for 5-(2-aminovinyl)isothiazole system in neutral solutions and also for 5-(aminomethyleneamino)1, 2, 4-thiadiazole system in acidic solutions. The rates were determined as the following, is e., for the former([28d]):_??_=6.21×10^-6s^-1, ΔH=12.2 k cal/mol, ΔS=41e. u.; for the latter ([26-H⁺]):_??_=10^6.4s^-1. Third, the formation of 10-S-4 sulfuranes were exemplified by the single crystal X-ray analysis for dibenzothiazocinium systems due to the 1, 5-transannular interaction between the sulfonio and the amino groups. The S-N bond lengths of the sulfuranes decrease and the sulfur atom gradually attains better TBP configuration according to the increase of electronegativity of the substituents at the sulfur. It is also shown that the electronic effect of the substituent at the sulfur was transmitted to the amino group through bond and/or through space by ¹H-and ¹³C-NMR measurements.