Ritter reactions. Part 4. Rearrangement of 3,3,7,7-tetramethyl-2,6-dimethylenebicyclo[3.3.1]nonane and crystal structure of 1-acetamido-2,2,5,6,6-pentamethyladamantane

Abstract

3,3,7,7-Tetramethyl-2,6-dimethylenebicyclo[3.3.1]nonane (3) was prepared by methylation of bicyclo[3.3.1]nonane-2,6-dione (1) followed by Wittig reaction. When the diene (3) was subjected to typical Ritter reaction conditions a 70% yield was obtained of a single compound whose structure was determined to be 1-acetamido-3,4,4,8,8-pentamethyladamantane (5) using X-ray diffraction methods. The crystal structure [P2₁/c, a= 7.091 (1), b= 23.398 (1), c= 9.651 (1), β= 95.79 (1), Z= 4] was shown to be disordered with a 4 : 1 ratio of enantiomers on the same site. Constrained refinement produced a final R= 0.054. A mechanistic pathway is proposed for this complex rearrangement involving the isolated intermediate 3,4,4,7,8,8-hexamethylbicyclo[3.3.1]nona-2,6-diene (8).