Formation by SRN1 Reactions and 1H N.M.R. Properties of Sterically Encumbered 2,4,6-Trialkylphenyl p-Nitrobenzyl Sulfides.

Abstract

Sterically hindered p-nitrobenzylic chlorides (1) and (2) react with the sodium salts of 2,4,6-trialkylbenzenethiols (3a)–(5a) by the S_RN1 reaction to give good yields of the corresponding p-nitrobenzylic aryl sulfides (6)–(10). For example, the reaction of sodium 2,4,6-triisopropylbenzenethiolate (4b) with α-t-butyl-a-methyl-p-nitrobenzyl chloride (2) gives the sulfide (10) in over 80% yield after 2 h at room temperature in Me₂SO. Only in reactions involving 2,4,6-tri-t-butylbenzenethiol (5a) are low yields or failed reactions encountered. Qualitative examination of the dynamic nuclear magnetic resonance spectra of the sulfides prepared in these reactions shows that up to three restricted rotational phenomena can be identified. These are rotation about the benzylic-carbon to p-nitrophenyl ring bond, rotation about the sulfur to aromatic ring bond, and rotation about the bond joining the t-butyl group to the benzylic carbon. The last phenomenon produces, in the sulfide (9), the relatively rare and unusual situation wherein the t-butyl group appears as three distinct methyl resonances at low temperatures.