Studies On The Effective Synthesis Of Alkynylphosphorous Compounds And Their Dehydrogenative Cyclization Reactions

Organophosphorus compounds are widely used in biomedicine,agriculture,new flame retardant materials,organic synthesis and asymmetric catalysis.Among them,the alkynyl phosphorus compounds(spC-P bonds)can be converted into a series of functional phosphorus compounds due to the unique carbon carbon triple bond and thus represents an important kind of organophosphorus compounds.The traditional methods for their synthesis mainly depended on the nucelophilic substitution reaction of phosphoryl halides and alkynyl metal reagents(alkynyl lithium/magnesium).However,the raw materials were highly moisture-sensitive,toixic and difficult to prepare.Moreover,the reaction condition was also harsh,thus indicating a narrow substrate scope.Subsequently,a number of substituted alkynes such as alkynyl copper,alkynyl sulfonic acid,alkynyl carboxylic acid or alkenes(1,1-dibromine olefins)were used to react with P(O)-H componds for preparing alkynylphosphorus compounds.There is no doubt that the direct dehydrogenative coupling between terminal alkynes and P(O)-H compounds is the most effective and ideal method to produce alkynyl phosphorus componds.In this paper,a series of alkynyl phosphine oxides were synthesized by palladium catalyzed spC-H/P(O)-H dehydrogenation coupling.The resulting alkynyl phosphine oxides were further allowed to react with hydrosilanes,delivering the corresponding triethylsilylphosphindole 1-oxide heterocyclic compounds via a free radical dehydrogenative cyclization process.The detailed contents and results come as follows:(1)A silver-free palladium-catalyzed dehydrogenative coupling reaction of various terminal alkynes and P(O)-H compounds was realized with use of the cheap acrylonitrile as a hydrogen acceptor,which overcame the disadvantages of previous works that must consume stoichiometric amount of noble silver saults.This synthetic method is economical,green,efficient and simple to handle.Both aromatic and aliphatic alkynes coupled readily with P(O)-H compounds under the reaction conditions.For example,aryl acetylenes including those bearing functional groups were transformed into alkynyl phosphine oxides successfully.The aliphatic terminal alkynes with active groups(such as OH,Cl,CN groups)also effectively coupled with the P(O)-H compounds.The reaction was scaled up to 10 mmol without any reduction of the efficiency,and the bioactive acetylene estrone was also efficiently phosphorylated by this method.(2)Using copper cyanide as a catalyst and tert butyl peroxide as an oxidant,some phosphorus indoles were synthesized by the free radical dehydrogenative cyclization of alkynyl phosphine compounds with trialkyl silanes.The exploitation of this reaction promotes the development and utilization of alkynylphosphorus componds.