CID Fragmentation of Deprotonated N-Acyl Aromatic Sulfonamides. Smiles-Type and Nitrogen-Oxygen Rearrangements

A general alkene aminoarylation enabled by N-centred radical reactivity of sulfinamides

Arylethylamines are popular structural elements in bioactive molecules but are often made through a linear series of synthetic steps. A modular protocol to assemble arylethylamines from alkenes in one step would represent a useful advance in discovery chemistry, though current limitations preclude a generally applicable method. In this work we disclose an aminoarylation of alkenes using aryl sulfinamide reagents as bifunctional amine and arene donors. This reaction features excellent regioselectivity and diastereoselectivity on a variety of activated and unactivated substrates. Using a weakly oxidizing photocatalyst, a nitrogen radical is generated under mild conditions and adds to an alkene to form a new C-N bond. A desulfinylative aryl migration event known as a Smiles-Truce rearrangement follows to form a new C-C bond. In this manner, arylethylamines can be rapidly assembled from abundant alkene feedstocks. Moreover, chiral information from the sulfinamide can be transferred via rearrangement to a new carbon stereocentre in the product, thus advancing the development of traceless asymmetric alkene difunctionalization.

Electrochemical cascade migratory versus ortho-cyclization of 2-alkynylbenzenesulfonamides

Efficient control over several possible reaction pathways of free radicals is the chemical basis of their highly selective transformations. Among various competing reaction pathways, sulfonimidyl radicals generated from the electrolysis of 2-alkynylbenzenesulfonamides undergo cascade migratory or ortho-cyclization cyclization selectively. It is found that the incorporation of an extra 2-methyl substituent biases the selective migration of the acyl- over vinyl-linker of the key spirocyclic cation intermediate and thus serves as an enabling handle to achieve the synthetically interesting yet under-investigated cascade migratory cyclization of spirocyclic cations.

Unexpected Gas-Phase Nitrogen-Oxygen Smiles Rearrangement: Collision-Induced Dissociation of Deprotonated 2-(N-Methylanilino)ethanol and Morpholinylbenzoic Acid Derivatives

A nitrogen-oxygen Smiles rearrangement was reported to occur after collisional activation of the PhN(R)CH2CH2O- (R = alkyl) anion, which undergoes a five-membered ring rearrangement to form a phenoxide ion C6H5O-. When R = H, such a Smiles rearrangement is unlikely since the negative charge is more favorably located on the nitrogen atom than the oxygen atom; hence, alternative neutral losses dominate the fragmentation. For example, collisional activation of deprotonated 2-anilinoethanol (PhN-CH2CH2OH) leads to the formation of an anilide anion (C6H5NH-, m/z 92) rather than a phenoxide ion (C6H5O-, m/z 93.0343). However, when the amino hydrogen of 2-anilinoethanol is substituted by a methyl group, i.e., 2-(N-methylanilino)ethanol, a Smiles rearrangement does occur, leading to the phenoxide ion, as the negative charge can only reside on the oxygen atom. To confirm the Smiles rearrangement mechanism, 2-(N-methylanilino)ethanol-18O was synthesized and subjected to collisional activation, leading to an intense peak at m/z 95.0385, which corresponds to the 18O phenoxide ion ([C6H518O]-). The abundance of the phenoxide ion is sensitive to substituents on the N atom, as demonstrated by the observation that an ethyl substituent results in the rearrangement ion with a much lower abundance. The nitrogen-oxygen Smiles rearrangement also occurs for various morpholinylbenzoic acid derivatives with a multistep mechanism, where the phenoxide ion is found to be predominantly formed after loss of CO2, proton transfers, breaking of the morpholine ring, and Smiles rearrangement. The Smiles mechanism is also supported by density functional theory calculations and other observations.

Electrochemical Migratory Cyclization of N-Acylsulfonamides

Benzoxathiazine dioxide, as a bioisostere of the clinically widely used diazoxide, exhibits interesting biological activity. However, limited success has been achieved in terms of its concise and direct synthesis. We report herein a facile electrochemical migratory cyclization of N-acylsulfonamides to access a diverse array of benzoxathiazine dioxides. The inclusion of electrochemistry is crucial for realizing such a novel transformation, which is substantiated both by the experiments and density-functional-theory calculations.