C-H activation with elemental sulfur: synthesis of cyclic thioureas from formaldehyde aminals and S8.
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.
Denk
M K
MK
Department of Chemistry, Erindale College University of Toronto, ON, Canada. mdenk@credit.erin.utoronto.ca
Gupta
S
S
Brownie
J
J
Tajammul
S
S
Lough
A J
AJ
D005557:Formaldehyde / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D010084:Oxidation-Reduction; D013455:Sulfur / Q000737:chemistry; D013890:Thiourea / Q000138:chemical synthesis*
D005557:Formaldehyde; D013455:Sulfur; D013890:Thiourea