Deaminative Heck-type Reactions Enabled By Visible Light Photocatalysis

Heck reaction is an important method to construct olefins,which was awarded the Nobel Prize in chemistry in 2010.However,the development of alkyl Heck reaction is not very mature compared with aryl or alkenyl Heck reaction,mainly because its alkyl sources are relatively limited.Therefore,it is very important to develop some new alkylation reagents.Aliphatic amines are a kind of common organic compounds.They are not only ubiquitous in many natural products,but also have developed a series of effective synthetic methods.Therefore,it is of great significance and value to construct new compounds efficiently from simple and easily available aliphatic amines by breaking carbon-nitrogen bonds.However,it is very challenging to break the C-N bond under mild conditions because the higher C-N bond can make the amino group difficult to be used as an effective leaving group.In this paper,we converted alkyl primary amines into redox-active alkyl pyridinium salts,and realized two kinds of deaminative Heck reaction under visible light photocatalysis.Firstly,we developed the deaminative Heck reaction of alkyl pyridinium salts with 1,1-diphenylethylene.The optimum conditions for the reaction were determined as following:Ir(4-Fppy)2(bpy)PF6 as photocatalyst,1,4-diazodicyclo[2.2.2]octane(DABCO)as base,acetonitrile(CH3CN)as solvent,at 40 0C.A series of polysubstituted styrene compounds were obtained with 34-97%isolated yields.For other olefins,such as cinnamic acid,alkenyl silicone ether and alkenylamine,corresponding products can also be obtained in 40-93%yields.Subsequently,we extended this strategy to the deamino-carbonyl Heck reaction.On the basis of the above reaction conditions,corresponding unsaturated ketones can be obtained in a general yield of 60-74%by applying 80 atm CO.All target products were confirmed and characterized by 1H NMR,13C NMR and HRMS.The spectral properties of target compounds were studied and their spectral data were preliminarily assigned.This research has been published on Angewandte Chemie International Edition(2019,58,2402).