Metal‐Free [3+2]‐Cycloaddition of Thiiranes with Isothiocyanates, Isoselenocyanates and Carbodiimides: Synthesis of 2‐Imino‐Dithiolane/Thiaselenolane/Thiazolidines

Abstract

Metal‐free regioselective [3+2]‐cycloaddition of 2‐aryl/alkylthiiranes with isothiocyanates, isoselenocyanates and carbodiimides is developed using BF2OTf⋅OEt2 to produce 2‐imino‐dithiolane/‐thiaselenolane/‐thiazolidine frameworks at room temperature. The selectivity, substrate scope and scale up are the important practical features.

Ring opening reactions of heterocycles with selenium and tellurium nucleophiles

“…Punniyamurthy and co-workers reported the construction of chalcogen-containing heterocycles exploiting the reactivity of thiiranes with isoselenocyanates. 51 The formation of 2-imino-thiaselenolanes 33 Scheme 32: Proposed reaction mechanism for the formation of 2imino-thiaselenolanes.…”

4‐Aryl‐2‐Imino‐1,3‐Dithiolanes from the Room Temperature Coupling of Sodium Dithiocarbamates with Sulfonium Salts

“…Note that cyclic dithiocarbamates are isomers of dithiolanes and their {SC=S} group is typically featured by a 13 C resonance at ca. 200 ppm, [32–36] whereas a diagnostic signal was found around 165 ppm in products spectra and assigned to the C=N moiety of dithiolanes [9,16] . All the IR spectra of prepared 2‐amino‐1,3‐dithiolanes display an intense absorption from 1590 to 1605 cm −1 due to the C=N stretching.…”

“…As for other synthetic procedures, the products were obtained as a mixture of E/Z isomers in an almost 1 : 1 ratio. [9,15–17,19] …”

“…Some documented synthetic methods to access 2‐imino‐1,3‐dithiolanes require starting materials difficult to handle due to their physical nature or their toxicity and corrosive character [9–12] . Furthermore, substituted 2‐imino‐1,3‐dithiolanes (or the corresponding iminium cations) have been obtained from dithiocarbamate salts and epoxides in the presence [13] or not [14] of BF 3 ⋅ OEt 2 as catalyst (Scheme 1A) or from the diiodine‐induced cyclization of S‐allyl dithiocarbamates (Scheme 1B) [4,15,16] .…”

“…Furthermore, substituted 2‐imino‐1,3‐dithiolanes (or the corresponding iminium cations) have been obtained from dithiocarbamate salts and epoxides in the presence [13] or not [14] of BF 3 ⋅ OEt 2 as catalyst (Scheme 1A) or from the diiodine‐induced cyclization of S‐allyl dithiocarbamates (Scheme 1B) [4,15,16] . Regioselective [3+2]‐cycloaddition of 2‐aryl/alkylthiiranes with isothiocyanates mediated by Pd catalysts in combination with a phosphine ligand, [17] a boron Lewis acid, [9] or triethylamine in hot DMF [18] has also been used to yield the 2‐imino‐dithiolane frameworks (Scheme 1C). On the other hand, a more simple strategy employing sodium dithiocarbamates in combination with 1,2‐dihaloalkanes as C 2 ‐synthons was reported in several papers, [19–21] however the procedures required the use of reflux conditions and additives such as K 2 CO 3 , NEt 3, or Br 2 (Scheme 1D).…”