| ?,?-Unsaturated carbonyl compounds are important synthons in organic synthesis,they are important raw materials to construct C-C bonds and C-heteroatom bonds.According to its electron cloud distribution,the ?-position is more electron-deficient and is more inclined to react with nucleophiles,thus Michael-type addition products are formed.However,there are relatively few studies on the ?-nucleophilic addition reaction of ?,?-unsaturated carbonyl compounds.The only two related reports so far are that after formation of radical at ?-position of carbonyl group,due to its electrophilic property,electron-rich aromatic hydrocarbons can work as nucleophiles to form ?-aryl addition products.The difficulty in realizing related reactions lies in the electrical polarity reversal at the ?-position of carbonyl group.By using photoredox strategy,it is possible to achieve such conversion.In this paper,around this issue,we have developed a series of reactions to achieve the ?-nucleophilic addition reaction.Mainly focus on the use of new type of photoreductant CBZ6 to reduce ?,?-unsaturated amides,thus a key radical at ?-position of carbonyl-will be formed,which can be captured by alcohols,water or hydrofluoric acid after further oxidation to form ?-nucleophilic adduct.In addition,the key radical intermediate in this reaction can be captured by electron-rich aromatic hydrocarbons to form ?-aryl addition products.The research content of this paper mainly includes the following three parts:1.The ?-oxygen nucleophilic addition to ?,?-unsaturated amides was discovered.By using our newly developed electon-rich non-push-pull electronic photoreductant CBZ6,alcohols and water can work as nucleophiles,selectively ?-oxygen addition to ?,?-unsaturated amides can be completed under visible light illumination.In this reaction,primary alcohols,secondary alcohols,water,deuterated water and heavy oxygen water can work well,44%-98%yields of desired products are obtained.When deuterium water is used as the substrate,?-deuteration rate is up to 94%.Various ?,?-unsaturated amides can also be applied to the reaction.According to the free radical capture experiment,?-TEMPO addition product can be isolated.It is confirmed that ?-hydrogen comes from the added nucleophiles when using deuterated water as nucleophile.These control experiments support the hypothetical reaction mechanism and identify the reaction occur via the carbocation at ?-position of carbonyl compounds.2.The ?-aromatic nucleophilic addition to ?,?-unsaturated amides was discovered.In the ?-oxygen nucleophilic addition reaction,a key radical intermediate at ?-position of carbonyl was confirmed.?-Aryl addition product would be formed if electron-rich aromatic hydrocarbons are used to capture this intermediate.The reaction has a wide application range for ?,?-unsaturated amides,and yields of 21%to 89%can be obtained.The reaction can work well for electron-rich aromatic hydrocarbons,while for electron-deficient aromatic hydrocarbons,such as triarylamine with ester substituents,the reaction got worse,only 21%yield of target product was obtained.In this reaction,it was verified that the catalyst was recyclable and the reactivity could be maintained.The free radical was tested during the reaction using EPR technology.3.The ?-fluorine nucleophilic addition to ?,?-unsaturated amides was discovered.In addition to alcohol,water and aromatic hydrocarbons,kinds of nucleophiles were tested and found that hydrofluoric acid,a weak nucleophile,could undergo ?-fluorine addition as well,with a yield ranging from 45% to 74%. |
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