The Research Of Gold-catalyzed Synthesis Of Allenes By Sulfur Ylides

Gold catalysts have been paid widely attention in recent years, they can activateolefins, alkynes and allenes to undergo multiple types of reactions efficiently andselectively. Cold catalysts can also catalyze the decomposition of diazo compounds togenerate ylides, which are important and active intermediates. Ylides can efficientlyprovide nucleophilic centers to attack the gold-activated unsaturated bond, which giverise to rearrangement or cyclization, and thus a new C-C bond or heterocycles areobtained. In the transition metal catalyzed ylides reactions, sulfur ylides have beenwidely used and the [2,3]-sigmatropic rearrangement is an important reaction in thisfield. The allenic compounds have important physiological and pharmacologicalactivities. Moreover, allenes are important intermediates of bioactive compounds anddrugs, and they have a wide rang of applications in the total synthesis of naturalproducts. This paper mainly focuses on gold-catalyzed synthesis of sulfur ylides bydecomposition of diazo compounds, which then undergo intramolecular[2,3]-sigmatropic rearrangement to afford allenes.In this paper, active gold carbene intermediates were obtained by gold-catalyzeddecomposition of diazo compounds, which then created with propargyl sulfide toproduce sulfur ylides, subsequent intermolecular [2,3]-sigmatropic rearrangement ledto the formation of corresponding allenes. Propargyl sulfide can be prepared fromaldehyde. By the systemic optimization of reaction conditions, the optimizedconditions are the use of5mol%IPrAuCl/AgNTf2,4equivalents of diazocompounds in toluene at reflux temperature under nitrogen atmosphere. We alsofound that gold catalyst with the large steric NHC ligand is superior, high temperatureand excessive diazo compounds could accelerate this reaction. The substrates withalkyl chain afford the product in higher yield, and the substituent on the sulfide have great impact on the yield too. Among all the diazo compounds we surveyed, ethyldiazoacetate and methyl diazophenylacetate are the best. Based on the literatures andthe experiments, We propose a mechanism that suldur ylides is the key intermediate,and [2,3]-sigmatropic rearrangement gives rise to the final products.