Chlorotrimethylsilane and Sodium Iodide: A Remarkable Metal‐Free Association for the Desulfurization of Benzylic Dithioketals under Mild Conditions

Abstract

A novel metal-free process allowing the reductive desulfurization of various benzylic dithioketals to afford diarylmethane and benzylester derivatives with good to excellent yields is reported. At room temperature, this mild reduction process requires only the use of TMSCl and NaI in CH2Cl2 and tolerates a large variety of functional groups.

Mild Deprotection of Dithioacetals by TMSCl/NaI Association in CH3CN

“…In CH 3 CN, we were pleased to isolate ketone 2a with a promising yield of 52 % (entry 7) with no trace of the reduced 2-ethylnaphthalene obtained in CH 2 Cl 2 . [17] Under same reaction conditions but without NaI, 1a was found unchanged showing the essential role of NaI (entry 8). Addition of water, NaOH aq.…”

“…First, we have selected 2-methyl-2-(naphthalen-2-yl)-1,3-dithiane 1a which was totally reduced into 2-ethylnaphthalene by TMSCl/NaI combination in CH 2 Cl 2 [17] as our model substrate to herein examine the dithiane deprotection reaction by the same reagents under a variety of reaction conditions (Table 1). In view of using EtOH as a green solvent, [19] we firstly try to deprotect 1,3-dithiane 1a in EtOH in the presence of 10 equiv.…”

“…Then, the case of diaryldithianes was examined. Under conditions A (TMSCl/NaI 10 equiv., r.t., 24 h), we observed that 1,3-dithiane 1r having no Hα, reacted with TMSCl/NaI to give a mixture composed in almost equal parts of the expected ketone 2r (43 %) accompanied by the reduction [17] product 1-benzyl-4methoxybenzene (40 %). To avoid the formation of the reduction by-product, we successfully replaced NaI by NaBr, increased the quantity of TMSCl/NaBr and heated the solution at 60°C for a prolonged time (TLC monitoring).…”

“…The methodology proposed herein is a good alternative to the existing methods since it does not use metals, oxidants, reducing agents, acidic or basic media, and keto-products were obtained in high to excellent yields. desulfurized at r.t. [17] in CH 2 Cl 2 using this metal-free process in a Mozingo-type reaction. [18] By replacing CH 2 Cl 2 by CH 3 CN as the reaction solvent, we surprisingly observed that dithianes derivatives were not reduced into methylene substrates but were totally and cleanly deprotected into ketones.…”

Mild Deprotection of Dithioacetals by TMSCl / NaI Association in CH3CN

“…In CH 3 CN, we were pleased to isolate ketone 2a with a promising yield of 52% (entry 7) with no trace of the reduced 2-ethylnaphthalene obtained in CH 2 Cl 2 . [17] Under same reaction conditions but without NaI, 1a was found unchanged showing the essential role of NaI (entry 8). Addition of water, NaOH aq or HCl aq had a deleterious effect on the reaction since a large part of 1a was recovered after 24 h of reaction (entries 9-12).…”