A General Thiolation of Magnesium Organometallics Using Tetramethylthiuram Disulfide

Abstract

The reaction of various functionalized aryl and heteroaryl bromides with i-PrMgCl·LiCl produces highly reactive Grignard reagents complexed by LiCl, which react with tetramethylthiuram disulfide [(Me₂NCS₂)₂] leading to the corresponding dithio­carbamates in excellent yields. Various transformations of the dithiocarbamates to thiols, thiol salts or thioethers have been ­demonstrated.

Key words

Grignard reactions - sulfur - chirality - lithium chloride - tetramethylthiuram disulfide

References

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5

The price of tetramethylthiuram disulfide is 30 Euro per kg (Aldrich).

9

The iodonaphthol derivative 5 has been obtained from the corresponding PhMe₂Si derivative by treatment with ICl.

10

We have treated also different alkyl magnesium compounds with TMTD in the presence of LiCl and have obtained corresponding thioderivates in excellent yields.

11

Typical Procedure: Preparation of 3-Trifluoromethyl-phenyl Dimethyldithiocarbamate ( 4a). A 25 mL Schlenk flask containing a i-PrMgCl·LiCl solution (10.5 mmol, 5.25 mL of 2.0 M solution in THF) was cooled to 0 °C, and 3-bromotrifluoromethylbenzene (10.0 mmol, 2.25 g) was added slowly at this temperature. The mixture was allowed to reach r.t. within 1.5 h. The exchange completion was determined by the GC analysis of an aliquot. The reaction mixture was cooled again to 0 °C and tetramethylthiuram disulfide (3, 9.5 mmol, 2.28 g) in dry CH₂Cl₂ (9.5 mL) was added at this temperature. After 2 h at r.t., the mixture was poured into sat. NH₄Cl solution (50 mL), the aqueous phase was extracted with CH₂Cl₂, the combined organic phases dried (MgSO₄), evaporated in vacuo and the residue recrystallized from CH₂Cl₂-heptane. Yield 2.12 g (84%), mp 83-84 °C.