An efficient and concise access to 2-amino-4H-benzothiopyran-4-one derivatives

摘要

A highly efficient and convenient protocol was developed to access 2-amino-4H-benzothiopyran-4-ones through a process of conjugated addition–elimination. The sulfinyl group was proved to be the optimum leaving group by thorough investigations on the elimination of sulfide, sulfinyl, and sulfonyl groups at the 2-position of benzothiopyranone. Most 2-aminobenzothiopyranones were obtained in good to excellent yields under refluxing in isopropanol within 36 h. This method is base-free and the substrate scope in terms of electronic properties of the substituents of the benzothiopyranone is broad. The ten grams scale-up synthesis of the representative compounds >4a and >4d was implemented to show the practical application of this reaction, which afforded the corresponding compounds in good yields and excellent chemical purity without requiring column chromatographical purification.