Reaction of essentially free benzyl cations with acetonitrile; synthesis of ethanimidic carboxylic anhydrides and unsymmetrical diacylamines
Benzyl cations were generated via the thermal decomposition of N-benzyl-N-nitrosopivalamide in acetonitrile and acetonitrile-water mixtures at 25 degrees C. The first-formed (primary) benzylating agent, the benzyl cation, was scavenged competitively by pivalate (trimethyl acetate) ion to yield benzyl pivalate, by acetonitrile to yield the corresponding N-benzylnitrilium ion, and by water (when present) to yield benzyl alcohol. The nitrilium ion underwent a cascade of reactions to yield an array of products whose identities and relative yields as a function of time were used to elucidate the mechanistic paths involved. Thus, the N-benzylnitrilium ion reacted with pivalate ion to yield the Z-isomer of N-benzylethanimidic pivalic anhydride, followed by its conversion into the E-isomer. This article appears to be the first to document compounds of this type. The E-isomer is labile under the reaction conditions, rearranging into N-acetyl-N-pivalylbenzylamine. In the presence of water as a diluent, a significant fraction of the nitrosoamide was hydrolyzed to benzyl alcohol; hydrolysis of the nitrilium ion yielded N-benzyl acetamide. The yield of hydrosylates was directly proportional to the mole fraction of water in the medium.
Darbeau
RW
Departments of Chemistry, McNeese State University, Lake Charles, Louisiana 70609 and The Johns Hopkins University, Baltimore, Maryland 21218, USA.
White
EH
Nunez
N
Coit
B
Daigle
M