C-H activation with elemental sulfur: synthesis of cyclic thioureas from formaldehyde aminals and S8

Chemistry. 2001 Oct 15;7(20):4477-86. doi: 10.1002/1521-3765(20011015)7:20<4477::aid-chem4477>3.0.co;2-i.

Abstract

The C-H activation of cyclic formaldehyde aminals LCH2 (L = RN-CH2CH2CH2-NR and RNCH2CH2-NR, R = Me, Et, iPr, tBu, or Ph) with S8 proceeds at unusually low temperatures (T< 160 degrees C) and results in the formation of the respective thioureas LC=S and H2S. The reaction constitutes a new, solvent-free method for the synthesis of thioureas that eliminates the toxic and highly flammable CS2. For R = tBu, the ionic carbenium thiocyanates [LCH]+ SCN- dominate the product spectrum and the respective thioureas are obtained in low yield. The reactivity of the analogous sulfur and oxygen ring systems towards S8 was investigated. 1,3-Dithiolane is cleanly converted into 1,3-dithiolane-2-thione (S8, 14 d, 190 degrees C) and resembles the cyclic formaldehyde aminals in this respect. 1,3-Dioxolane (L = OCH2CH2O) is completely inert towards sulfur even under forceful reaction conditions (190 degrees C, 14 d). The formation of thioureas from aminals was investigated at the CBS-4 and B3LYP/6-31G(d) levels of theory.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Formaldehyde / chemistry
  • Models, Molecular
  • Molecular Structure
  • Oxidation-Reduction
  • Sulfur / chemistry
  • Thiourea / chemical synthesis*

Substances

  • Formaldehyde
  • Sulfur
  • Thiourea