THERMAL FISSION OF HYDROXYLAMINE DERIVATIVES WITH NEIGHBOURING-GROUP-PARTICIPATION BY THIOETHER FUNCTIONS: PREPARATION OF 1,2-BENZISOTHIAZOLES

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Abstract
Some of the factors influencing the preparation of 1,2-benzisothiazoles from 2-(alkylthio)phenyl-substituted oximes are discussed. Good yields of 3-aryl-1,2-benzisothiazoles 4 may be obtained from readily available precursors. Reaction takes place under particularly mild conditions when a t-butylthio function is situated anti to the leaving group at oxime-nitrogen and S—N overlap is not restricted by ring-strain in the transition-state. The corresponding N-methyl-hydroxamic acid derivatives 2 give good yields of 2-methyl-1,2-benziso-thiazol-3(2H)-one 13 only when a t-butylthio substituent is present, e.g. in 2f. The ethylthio- and i-propylthio-analogues 2d and 2e give the vinylthioethers 12, while the methylthio derivatives 2a-c undergo a novel rearrangement to “Pummerer'' esters 11. The preparation of the polycyclic compounds fluoreno-[9,9a,1-cd]-1,2-thiazole 7 and 2,2′-bi(2H-fluoreno[9,9a,1-de]-1,3-thiazine) 8 is described.