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A catalyst based on iron and elemental sulfur has been shown to efficiently promote a redox-neutral reaction between 2-nitrophenols and 2,6-disubstituted p-cresols, allowing for the preparation of 2-arylbenzoxazoles in good yields. This synthetic methodology also affords high atom economy without the use of any external oxidizing and/or reducing reagents. This is the first redox–condensation reaction of 2-nitrophenols with 2,6-disubstituted p-cresols.

4,6-Diaminoresorcinol, which is a raw material of ZYLON (PBO fiber), has an instability in air atmosphere. Therefore, very stable benzo[1,2-d:5,4-d']bis-2(3H)-oxazolone recognized a useful equivalent of 4,6-diaminoresorcinol during the stages of production, storage, and transportation. By combining the sulfur-assisted carbonylation of 4,6-diaminoresorcinol dihydrochloride with carbon monoxide and triethylamine under 0.1 MPa at 20°C for 4 h in DMF with the oxidation of resulting hydrogen sulfide salt with molecular oxygen for 2 h, benzo-[1,2-d:5,4-d']bis-2(3H)-oxazolone was obtained in a quantitative yield. Also, carbonylation of 2,5-diaminohydroquinone dihydrochloride and 2,5-diamino-1,4-benzenedithiol dihydrochloride was smoothly performed to give benzo[1,2-d:4,5-d']bis-2(3H)-oxazolone and benzo[1,2-d:4,5-d']bis-2(3H)- thiazolone, respectively, in good to excellent yields under similar reaction conditions. Furthermore, 2,6-dimercaptobenzo[1,2-d:5,4-d']bisoxazole, which is another equivalent of 4,6-diaminoresorcinol, was obtained in excellent yield by the thiocarbonylation of 4,6-diaminoresorcinol dihydro-chloride with carbon disulfide in the presence of 1-methylpyrrolidine at 20°C for 24 h in DMF. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 23:111–116, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20746

With ambient pressure of carbon monoxide and oxygen at room temperature, N,N-dialkyl-N'-arylureas were selectively accessible from secondary amines, aromatic amines, and sulfur in good to excellent yields. For example, N-butyl-N-methyl-N'-(3,4-dichlorophenyl)urea, which is used as a herbicide (neburon), was afforded successfully from butylmethylamine (2 equiv), 3,4-dichloroaniline (1 equiv) and sulfur (1 equiv) in 79% (21.8 g) yield using carbon monoxide (0.1 MPa) and oxygen (0.1 MPa) at 20 °C in DMF.

The first example of cyclic urea synthesis from secondary amines by the use of sulfur-assisted carbonylation and oxidation was established. By combined sulfur-assisted carbonylation of secondary α,ω-diamines under an ambient pressure of carbon monoxide at 20°C with oxidation by molecular oxygen (0.1 MPa, 20°C), a facile synthetic method for N,N′-dialkyl cyclic ureas including 1,3-dimethyl-2-imidazolidinone was developed. © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:64–68, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20508

A solvent-free carbonylation and oxidation system aimed at green and sustainable chemistry was developed. With these reactions, an environmentally benign synthesis of urea derivatives could be carried out in good to excellent yields from primary amines and sulfur at ambient pressure of carbon monoxide and oxy-gen. For example, N, N′-dioctylurea was prepared in 99% yield from two equivalents octylamine and one equivalent sulfur in the presence of carbon monoxide (1 atm) at 80 °C and oxygen (1 atm) at room temperature, in the complete absence of solvent.

A new and facile synthetic method for urea derivatives was developed under mild conditions, and contrasts with conventional preparation methods that need highly toxic reagents (phosgene) or severe reaction conditions. In our reaction system, N,N-dimethylformamide or dimethyl sulfoxide as solvent strongly accelerated the carbonylation of primary amines with sulfur under carbon monoxide (1 atm) at 20 °C to give the corresponding thiocarbamate salts. These salts were readily oxidized by molecular oxygen under similarly mild conditions to afford urea derivatives in good to excellent yields. This urea synthesis could also be applied to a new synthesis of aromatic ureas by use of 1,8-diazabicyclo[5.4.0]undec-7-ene in N,N-dimethylformamide.

Substitution of 2,6-di-tert-butyl-p-cresol (II) by 2-tert-butyl-p-cresol, 2,6-dimethoxy-p-cresol or 1-tert-butyl-toluene results in the isolation of the corresponding products in small or trace amounts only.

The compound (III) is the stable equivalent to the instable compound (I), which is a raw material of ZYLON.

The glycerol carbonate synthesis from glycerol, which is an inevitable by-product of biodiesel production, was established. By combined sulfur-assisted carbonylation of glycerol under 1.0 MPa of carbon monoxide at 80°C in DMF with oxidation by copper bromide(II), a facile synthetic method for glycerol carbonate in good yield was developed. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:99–102, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20583

The first example of cyclic urea synthesis from secondary amines by the use of sulfur-assisted carbonylation and oxidation was established. By combined sulfur-assisted carbonylation of secondary α,ω-diamines under an ambient pressure of carbon monoxide at 20°C with oxidation by molecular oxygen (0.1 MPa, 20°C), a facile synthetic method for N,N′-dialkyl cyclic ureas including 1,3-dimethyl-2-imidazolidinone was developed. © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:64–68, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20508

A solvent-free carbonylation and oxidation system aimed at green and sustainable chemistry was developed. With these reactions, an environmentally benign synthesis of urea derivatives could be carried out in good to excellent yields from primary amines and sulfur at ambient pressure of carbon monoxide and oxy-gen. For example, N, N′-dioctylurea was prepared in 99% yield from two equivalents octylamine and one equivalent sulfur in the presence of carbon monoxide (1 atm) at 80 °C and oxygen (1 atm) at room temperature, in the complete absence of solvent.

A novel convenient method for the generation of thiocarbonyl ylides from readily accessible starting materials and the first synthetic application of in situ generated ylides in the synthesis of silyl enol and dienol ethers, accompanied by C-C bond formation, is described. Under completely neutral conditions without any catalyst or additive, thermal reactions of S-alpha-silylbenzyl thioesters in sealed tubes at 180 degrees C provided silyl enol and dienol ethers in good to excellent yields with high stereoselectivities. This procedure consists of a multistep reaction in a one-pot process, i.e., 1,4-silatropy of S-alpha-silylbenzyl thioesters to give thiocarbonyl ylides, 1,3-electrocyclization of the ylides to give thiiranes, and the extrusion of sulfur from thiiranes to give silyl enol and dienol ethers.