AgBF₄-Catalyzed Oxa-Diels-Alder Reaction And A Catalyst Free Curtius Like Rearrangement And Degradation Reaction Of Sulphuryl Azides

The oxa-Diels-Alder reaction of aldehydes with 1,3-dienes is of great interest because it can lead to six-membered heterocyclic compounds in a single step, and is useful in the synthesis of many natural products and physiologically active compounds. Numerous reported oxa-Diels-Alder reactions have used activated 1,3-dienes such as Danishefsky’s diene or electron-deficient aldehydes such as glyoxylic acid derivatives. For the reactions of unactivated aldehydes with electrically neutral 1,3-dienes however, it is often necessary to use a strong Brensted acid or a Lewis acid to interact with an aldehyde through a mono-coordination model, leading to reactions with low functional group tolerance.Silver catalysts have been largely ignored by organic chemists for many years, but the efficiency that they show in many organic synthetic reactions is clear. Because of their favorable redox potential (the reduction potential of silver(I) is 0.8 eV) and mild Lewis acidity, silver-based catalytic reactions are likely to have good functional group tolerance.Here, we report that AgBF4 catalyzes oxa-Diels-Alder reactions of electrically neutral dienes and unactivated aldehydes under mild and convenient conditions. Additionally, with the assistance of the heteroatoms in β-position of aryl aldehydes or acrolein derivatives through a bi-coordination model, the high selective oxa-Diels-Alder reaction can be achieved under milder reaction conditions and with broader substrate scope.The Curtius rearrangement--the degradation of an acyl azide into an isocyanate through a concerted mechanism-is a broadly useful method for the synthesis of amine from carboxylic acids, and the isocyanate can also be trapped by variety of other nucleophiles, including alcohols and amine, which provides the corresponding carbamate and urea, over 1000 reference can be found in the literature related to the Curtius rearrangement. But almost all these reactions were using acyl azides. There were very few reports about the Curtius rearrangement of phosphoryl azides. And the Curtius rearrangement of sulphuryl azides was only reported in some theoretical researches about photolysis by using UV.In recent years, sulphuryl azides have been demonstrated with interesting synthetic utility, including metal-catalyzed C-H amination and click chemistry. So it is very interesting and challenging to develop a Curtius rearrangement of sulphuryl azides to enlarge the applications of them.Herein we report a Curtius like rearrangement reaction cascade a degradation reaction of sulphuryl azides to form C-C bonds, in which the sulphuryl azides were prepared from disubstituted amines in one step. The reaction has broad substrate range, good functional group tolerance, does not need any catalyst, affords products in good yields.