Abstract
AbstractThree‐dimensional aza‐analogues of 1,2‐benzothiazine 1,1‐dioxides have been prepared from sulfonimidamides. Two different protocols are presented. The first is a rhodium‐catalyzed annulation reaction with α‐sulfonyloxyketones leading to 4‐unsubstituted benzothiazine derivatives. By selective bromination with NBS the heterocyclic ring can further be functionalized. In the second approach, an iridium catalyst is applied under solvent‐free mechanochemical conditions providing products with 3,4‐disubstituted thiazine rings from diazoketo esters and diazoketo sulfones.magnified image
Highlights
Following the idea of bioisosteric replacement as a key concept in medicinal chemistry,[6] analogues benzo-fused sulfoximines B (Scheme 1) have caught the attention of the community[7,8] leading to the development of a range of protocols for their synthesis.[9]
With the vision and intention to extend the chemistry of such hexavalent sulfur compounds, we wondered about cyclic sulfonimidamides (Scheme 1, bottom), which, to the best of our knowledge, have yet remained unstudied.[11,12]
Benzothiazine 1-oxides started from a protocol for a rhodium catalysis leading to sulfoximines introduced by Glorius.[9i]. In a subsequent study, we had demon
Summary
Scheme 1. (Top) various types of 1,2-benzothiazines A–C and selected examples of bioactive benzo-fused sultams A1–A3; (bottom) synthetic strategy towards development of various 1amino-1,2-benzothiazine 1-oxides described here. In the context of sulfoximine and sulfondiimine chemistry,[9b,10] we had developed rhodium catalyses for CÀ H bond functionalizations with 2-diazo-3-oxo esters 10 as coupling partners providing heterocyclic products in high yields In light of these results, analogous reactions of with sulfonimidamides 1 were expected to lead to 1,2benzothiazines characterized by structural variability at position 3 and carboxyl or sulfonyl groups at position 4 of the heterocycle. Assuming that elevated temperatures were problematic due to substrate decomposition, an alternative protocol was searched for In this context, the findings by Pawar, who was able to couple sulfoximines with diazoketones under iridium catalysis at room temperature, caught our attention.[9a] Transferring these conditions with [Cp*IrCl2]2 (2.5 mol %) as catalyst and PivOH (2.0 equiv.) as additive in TFE to the reaction of sulfonimidamide 1 a and diazoketone a provided product aa in 34% yield (Table 2, entry 8). While para-tolyl-substituted derivative 1 b reacted with a to give 1,2-benzothiazine ba in 90% yield,
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