Replaced By The Ring Opening Reaction Of Preparation Of Ammonia Sulfur Heterocyclic Propane, Taurine

Recently, taurine (2-aminoethanesulfonic acid) and substituted taurines have attracted more and more synthetic interests because they are involved in various and important physiological processes. It has been demonstrated that taurine and its cyclic analogues show many physiological activities.In our previous work, a series of aliphatic 1,1-disubstituted taurines were synthesized from aliphatic 2,2-disubstituted thiiranes via the direct ammonia ring-opening reaction in the presence of silver nitrate and subsequent peroxy acid oxidation. Comparison with previous dibenzylamine ring-opening method, the direct ammonia ring-opening method is a more atom-economic one. Based on the direct ammonia ring-opening method, 1-substituted taurines were synthesized atom-economically from 2-substituted thiiranes. On the other hands, the regioselectivity of aliphatic and aromatic thiiranes in the ammonia ring-opening reaction have been investigated.Firstly, 6 various disubstituted epoxides were synthesized from the corresponding aldehydes and ketones via the modified Corey-Chaykovsky epoxidation. And 11 structurally diverse substituted epoxides were converted to the corresponding thiiranes via the reaction with thiourea referring a modified literature method in moderate to good yields (30–98%). It has been found that thiourea is a more efficient and convenient oxygen-sulfur changing reagent than potassium isocyanate and silica gel-absorbed potassium isocyanate in the episulfidation.Secondly, a series of 1-substituted taurines were prepared from corresponding 2-substituted thiiranes via the ring-opening reaction in the presence of silver nitrate with ammonia-methanol solutions and subsequent hydrogen sulfide desilverization and peroxy acid oxidation. Three of them are new compounds and their structures were confirmed by IR, 1H NMR, 13C NMR and HRMS.Finally, the regioselectivity of aliphatic and aromatic mono- and disubstituted thiiranes in the ammonia ring-opening reaction have been investigated. The results indicated that all aromatic substituted thiiranes give rise to aromatic 2-substituted or 2,2-disubstituted taurines compared with aliphatic substituted thiiranes, revealing that all silver-coordinated aliphatic thiiranes were attacked on their less substituted ring carbon atom due to less steric hindrance. Their regioselectivity are controlled by steric effect, whereas all silver-coordinated aromatic substituted thiiranes (including monoaryl and diarylthiiranes) are attacked on their more substituted ring carbon atom in the ring-opening reaction because the benzylic cations could be stabilized by the aromatic rings through the p-πconjugative effect in the tranbsition state in the ring opening reaction. The regioselectivity of aromatic substituted thiirane in ring-opening reaction is controlled by the electronic effect. Four aromatic 2-monosubstituted and 2,2-disubstituted taurines were synthesized from corresponding arylthiiranes.