Reactions of 2,4,6-Tri-t-butylnitrosobenzene with Grignard Reagents

Reactions of 2,4,6-tri-t-butylnitrosobenzene (1) with alkylmagnesium halides afforded 6-alkyl-1-hydroxy-imino-2,4,6-tri-t-butyl-2,4-cyclohexadienes (2), 4-alkyl-1-hydroxyimino-2,4,6-tri-t-butyl-2,5-cyclohexadienes (3), and N-alkyl-2,4,6-tri-t-butylanilines (4) depending on the Grignard reagents used. The distribution of the reaction products indicated that the oximes were formed via an attack of the anionic species on the ortho- and the para-carbons, respectively, to the nitroso group, but that the N-alkylanilines via a free radical mechanism involving an electron transfer from the Grignard reagent to 1. The free radical mechanism was confirmed in the case of t-butylmagnesium chloride by trapping the t-butyl radicals as 1-t-butoxyimino-2,4,4,6-tetra-t-butyl-2,5-cyclohexadiene (8). Such a mechanistic difference has been explained in terms of the difference in electron affinities of the free radicals derived from Grignard reagents.