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C−H Activation with Elemental Sulfur: Synthesis of Cyclic Thioureas from Formaldehyde Aminals and S 8
Author(s) -
Denk Michael K.,
Gupta Shilpi,
Brownie John,
Tajammul Sabiha,
Lough Alan J.
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20011015)7:20<4477::aid-chem4477>3.0.co;2-i
Subject(s) - chemistry , sulfur , formaldehyde , medicinal chemistry , solvent , yield (engineering) , dithiolane , butane , reactivity (psychology) , organic chemistry , polymer chemistry , catalysis , materials science , medicine , alternative medicine , pathology , metallurgy
The C−H activation of cyclic formaldehyde aminals LCH 2 (L=RN‐CH 2 CH 2 CH 2 ‐NR and RNCH 2 CH 2 NR, R=Me, Et, i Pr, t Bu, or Ph) with S 8 proceeds at unusually low temperatures ( T <160 °C) and results in the formation of the respective thioureas LC=S and H 2 S. The reaction constitutes a new, solvent‐free method for the synthesis of thioureas that eliminates the toxic and highly flammable CS 2 . For R= t Bu, 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 S 8 was investigated. 1,3‐Dithiolane is cleanly converted into 1,3‐dithiolane‐2‐thione (S 8 , 14 d, 190 °C) and resembles the cyclic formaldehyde aminals in this respect. 1,3‐Dioxolane (L=OCH 2 CH 2 O) is completely inert towards sulfur even under forceful reaction conditions (190 °C, 14 d). The formation of thioureas from aminals was investigated at the CBS‐4 and B3LYP/6‐31G(d) levels of theory.