Beckmann Rearrangements of 1-Indanone Oxime Derivatives Using Aluminum Chloride and Mechanistic Considerations

Hydrocarbostyril, which is a key intermediate in our new synthetic route to 6-nitroquipazine, can be prepared from 1-indanone oxime by Beckmann rearrangement. We have optimized the reaction by using a Lewis acid, aluminum chloride, in the yield of 91% instead of common acids such as polyphosphoric acid, and sulfuric acid used in conventional Beckmann rearrangement (20% in the literature, 10% in our experiment). The optimized condition is established by using three equivalents of aluminum chloride in CH2Cl2 at -40 C room temperature for 40 min. We have applied this condition to other 1-indanone derivatives, such as 4-methyl-, 4-methoxy-, 4-nitro and 6-nitro-1-indanones. The mechanism of this BR has been proposed on the basis of the effect of temperature and substituent on product ratio, with the aid of PM3 calculation for a model system.