The Mechanism of the ortho‐Methylation of Nitrobenzenes by Dimethylsulfonium Methylide

Abstract

Nitrobenzenes carrying an ortho substituent are selectively methylated at the free ortho position by reaction with dimethylsulfonium methylide. The importance of the ortho substituent is demonstrated by the failure of the methylation of nitrobenzene and 3-and 4-nitroanisole. This is explained by the out-of-plane geometry of the nitro group in the orthosubstituted derivative, which enables a specific interaction

Concerning the deprotonation of the trimethylsulfonium ion by the dimethylsulfinyl anion

“…For spectral data see ref. 4. The presence of 5% D in the 3-methyl group follows from a weak triplet signal at 2.27 ppm overlapping with the strong singlet signal for CH 3 at 2.29 ppm in the 1 H NMR spectrum and a corresponding increase of the M + 1 satellite peak in the EI spectrum.…”

“…In a more recent application, Kitano and Ohashi 3 reported on the nucleophilic ortho-methylation of ortho-substituted nitrobenzenes by action of 2. Based on deuterium labelling experiments, 4 we could show that the reaction proceeds essentially according to the concept of vicarious nucleophilic substitution. 5 The reaction sequence is outlined for 2-nitroanisole (3) as substrate in Scheme 1.…”

“…Intriguingly, we observed an almost complete deuterium depletion of the transferred methylene group of octadeuteriodimethylsulfonium methylide ([D 8 ]2) when the perdeuteriated sulfur ylide was prepared from [D 9 ]1 with the dimethysulfinyl (dimsyl) carbanion (8) as base in DMSO. 4 By way of contrast, the dideuteriated methylene group was introduced intact into 7 when [D 9 ]1 was deprotonated by sodium hydride in DMF.…”

“…Because the deprotonation of sulfonium ions by the dimsyl anion in Scheme 1 The nucleophilic ortho-methylation of 2-nitroanisole (3) by dimethylsulfonium methylide (2). 4 DMSO is the classical protocol for the generation of sulfur ylides, 2 it is of some interest to obtain deeper insights into this process. In the present article, the results of 13 C-and D-labelling experiments are presented and a mechanism is suggested to account for the unexpected hydrogen exchange that accompanies the deprotonation of the trimethylsulfonium ion (1) by the dimsyl anion (8).…”

Beyond the Corey Reaction II: Dimethylenation of Sterically Congested Ketones

“…The experimentally known C-methylenations of nitrobenzene , and anthracene with DMSM (TSs M and N , Figure ) were engaged for comparative analysis. Due to the σ–π attractions between the methyl groups of DMSM and the aromatic rings, the barriers for the methylenation strongly depend on computational method (Figure ).…”