Beckmann Fragmentation and Rearrangement. Part VII. Fragmentation and cyclization of α-methylthio-ketoximes. Fragmentation reactions no. 27

✍ Scribed by Cyril A. Grob; Junya Ide

• Publisher: John Wiley and Sons
• Year: 1974
• Tongue: German
• Weight: 813 KB
• Volume: 57
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19740570833

✦ Synopsis

Abstract

α‐Methylthio‐propiophenone anti‐oxime p‐toluenesulfonate (tosylate) (12b) fragments quantitatively in 80% ethanol yielding benzonitrile and a methylidenesulfonium ion 15. The syn‐isomer, however, undergoes a Beckmann rearrangement. The fragmentation of α‐methylthio‐isobutyropher one anti‐oxime tosylate (13b) is accompanied by cyclization to the 1, 2‐thiazetin‐1‐ium ion 27, which is hydrolyzed via the sulfimine 29 to the keto sulfide 20 and the keto sulfoxide 30. A comparison of the rates of the α‐alkylthio anti‐ketoxime tosylates 12b and 13b and of the homomorphous oxime tosylates 16b and 17b shows that fragmentation and cyclization are strongly assisted by the sulfur atom. Whereas both the anti‐ and syn‐isomers of α‐amino ketoxime derivatives fragment quantitatively, only the anti‐isomers of α‐alkylthio ketoxime derivatives undergo facile fragmentation.