Organocatalytic Cyclization Reaction Using Carbonyl Sulfide

Carbonyl sulfide(COS)is an important intermediate of the atmospheric sulfur cycle and one of the main sulfur-containing impurities in syngas.COS is widely released from volcanic eruptions,deep-sea hydrothermal and industrial production.COS in the atmosphere is easily oxidized to form sulfuric acid in the stratosphere,which further forms acid rain to harm the environment.In recent years,the emission of COS from human production and life is also increasing sharply,so the problem of COS fixation and chemical utilization has become an important research direction of green chemistry.Heterocyclic skeletons containing oxygen,nitrogen and sulfur atoms are ubiquitous in synthetic medicines,biomolecules and natural products.In particular,five-membered heterocyclic compounds,such as thiocarbonates and thiazolidinone derivatives,have attracted extensive attention in pharmaceuticals and organic synthetic chemistry as bioactive substances and intermediates.Up to now,the reaction systems for the construction of heterocyclic molecule employed COS as substrate are limited.This paper focuses on the design and synthesis of novel organocatalytic systems for COS activation and chemical transformation to selectivley synthesize high value-added five-membered heterocyclic compounds.(I)The synthesis of strong nucleophilic highly polarized olefin tetrahydropyrimidin-2-ylidene(THPEs)was realized using commercially available organic amine 1,5-diazabicyclo[4.3.0]non-5-ene as a starting material.The organic small molecule THPEs can effectively capture COS under room temperature and atmospheric pressure and obtain corresponding THPEs-COS adducts,which were characterized by NMR,IR,MS and X-ray single crystal diffraction.The single crystal data showed that the O-C-S angles in the THPEs-COS adducts are in the range of 126.7(2)~127.41(1)~o,which indicates that THPEs could effectively activate COS.(II)We report a THPEs-COS adducts organocatalyzed cyclication of COS with propargylic alcohols/amines/amides to selectively synthesize various 1,3-oxathiolane-2-ones,1,3-thiazolidine-2-ones and 1,3-thiazolidine-2,4-diones derivatives under mild reaction conditions,and a variety of functional groups are well-tolerated with high selectivity.Further,a series of analytical methods,including NMR,IR and isotope labeling methods were used to investigate the proposed mechanism.The results show that THPEs-COS adduct as a nucleophilic reagent initiated the cyclization of propargylic alcohols with COS,and the activated COS was involved in the construction of heterocyclic compounds.However,in the cyclization of propargylic amines/amides with COS,THPEs-COS adduct acted as an organic base to activate N-H bond of substrates,and free COS is involved in the construction of heterocyclic compound.In addition,using COS as a sulfur source,the insulin sensitizer rosiglitazone was effectively obtained by this alternative route.In conclusion,a novel organic system was designed and synthesized for the cyclization of COS with functionalized propargyl derivatives to effectively prepare high value-added sulfur heterocyclic compounds with selectivity,which provided a new way for the green transformation of COS.