Expeditious Method for Synthesis of Symmetrical 1,3‐Disubstituted Ureas and Thioureas

Broad Scope and High‐Yield Access to Unsymmetrical Acyclic [11C]Ureas for Biomedical Imaging from [11C]Carbonyl Difluoride

“…We concluded that the homocoupling of aniline with [ 11 C]carbonyl difluoride to form the urea [ 11 C] 3 via the isocyanate [ 11 C] 2 was mediated rapidly by water during the reaction quench. This conclusion accords with a study showing that ureas may be rapidly synthesized from isocyanates in high yields in cold (4‐5 °C) water, [17] and reports of the promoting effect of bulk [18] or trace water [19] on symmetrical urea synthesis from isocyanates, including that of [ 11 C]1,3‐bis(2‐chloroethyl)urea [13b]…”

“…Although there is as yet no prominent example, some symmetrical [ 11 C]ureas could become candidate PET radiotracers, and efficient methods for their radiosynthesis is therefore of some interest. Tertiary amines and heterocyclic amines have been shown to improve the yields of symmetrical diaryl ureas from isocyanates [19] . Therefore, we investigated whether pyridine could promote homocoupling of aniline to produce symmetrical [ 11 C] 3 .…”

“…Tertiary amines and heterocyclic amines have been shown to improve the yields of symmetrical diaryl ureas from isocyanates. [19] Therefore, we investigated whether pyridine could promote homocoupling of aniline to produce symmetrical [ 11 C]3. Use of 1 μmol of pyridine and 2 μmol of aniline in acetonitrile (0.5 mL) gave a moderate yield of [ 11 C]3 (Table 1, entry 3).…”

Acyclic and Cyclic Ureas (Update 2013)

“…Treating isocyanates with a tertiary amine such as triethylamine as a catalyst, in 1,4-dioxane at room temperature, gives rise to the formation of the corresponding symmetrical ureas. [28] 18. 8 Thioureas formed by reaction of isothiocyanates with secondary amines can be converted into ureas 4 without workup by treating the initially formed products with 50% aqueous hydrogen peroxide (Scheme 3).…”

ZrOCl2.8H2O: An Efficient Catalyst for the Synthesis of N,N?-Disubstituted Ureas from Biuret Under Solvent Free Conditions

“…Several urea derivatives are used as plant growth regulators, herbicides, pesticides, corrosion inhibitors, antioxidant, dyes for cellulose fibers, antidiabetic and tranquillizing drugs [12][13][14] . A large number of methods are reported for the synthesis of urea derivatives including oxidative 15 and reductive carbonylation 16 of amines, reaction of amines with phosgene and its derivatives 11,17 , carbmates 18 , isocynates 19 , or by reaction of urea or thiourea with amines 20 . Different catalytic systems are also reported for synthesis of urea derivatives such as iodine 21 , zinc chloride 22 , Cs 2 CO 3 23 , titanium (IV)isopropoxide and sodium borohydride 24 , CeCl 3 .7H 2 O-KI 25 , PEG-400 26 and zeolite HSZ-360 14 .…”