Solvolysis of trimethylsilyl-N-aryl carbamates

The kinetics of the solvolysis reaction of various trimethylsilyl esters of N-aryl carbamic acid with isopropanol was studied. UV spectrophotometry was used to monitor the reaction and the pseudo first order rate constants were determined. The experiments were carried out in dioxane solutions containing lithium chloride. A reaction mechanism is suggested on the basis of the dependence of the reaction rate on ionic strength, the parameters of activation, the reaction constant (ϱ) and the isotope effect.     

Atropisomerism of aromatic carbamates

ortho‐Haloarylcarbamates like 1 – 4 show a high rotational barrier about the N? aryl bond of up to 91.6 kJ mol^?1 as found for 1 , which was determined by 2D exchange NMR spectroscopy (EXSY). It was further demonstrated that the height of the barrier not only depends on the substituents at the axis of chirality, but is also influenced by electronic effects.     

Amidation through carbamates

N-Alkyl carbamates of primary amines are easily converted into amides under treatment with Grignard reagents. Consequently, primary amines can be converted into amides in a one-pot reaction through carbamate protection and Grignard addition.     

三苯基锗氨荒酸酯的合成

合成了10个新的三苯基锗氨荒酸酯类化合物,利用元素分析,IR、^1HNMRMS表征了它们的结构。部分化合物初步生物活性测试结果表明,该类化合物对KB,HCT和Bel癌细胞具有较好的抑制活性。     

Scleroglucan derivatives: Aromatic carbamates

Scleroglucan is a polysaccharide produced industrially by the fungus Sclerotium rolfsii. Aromatic carbamate derivatives of scleroglucan have been prepared via the reaction of phenyl and tolyl isocyanates on the hydroxyl groups of the polymer chain. The reaction conditions have been determined in order to obtain the fully substituted polymer while conserving as much as possible the initial chain length. The reaction in pyridine at 80°C of a large exess of isocyanate (three times the stoechiometric amount) yields the higher degree of substitution (DS) and the higher intrinsic viscosity. These new polymers have been characterized by elemental microanalysis, spectroscopic methods (IR, ¹H-, and ¹³C-NMR) and thermal analysis. They are found to be soluble in organic solvents and soften between 200 and 225°C, and are thermally unstable above this temperature. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3187–3192, 1999     

Reactions of hexaorganyldigermoxanes with O-trimethylsilyl carbamates

Hexa-n-butyl- and hexaisopentyldigermoxanes but not hexaphenyldigermoxane react with O-trimethylsilyl N,N-diethylcarbamate and trimethylsilyl piperidinocarboxylate to give O-triorganylgermyl carbamates.     

Electron-impact induced rearrangement of N-acetyl-O-aryl carbamates

Electron-impact induced rearrangements of a series of agriculturally important carbamates and N-acyl carbamates are described. High resolution and metastable evidence supporting this is presented.     

Reactions of stannyl carbamates with organochlorosilanes

Rapid and exothermic reactions of stannyl carbamates with organochlorosilanes result in cleavage of the Sn-O-C bond and afford silyl carbamates in a high yield.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 313–314, February, 1994.     

The regioselective aminohydroxylation of allylic carbamates

The synthesis and aminohydroxylation of a series of acyclic allylic carbamates is described: the formation of a putative O=Os=NR linkage between the transition metal and substrate is proposed to account for the high levels of regioselectivity that were observed; proof of the structure of one of the aminohydroxylation products was obtained through X-ray crystallography.     

Catalytic enantioselective conjugate addition of carbamates

Catalytic, asymmetric conjugate addition of carbamates to enoyl systems has been realized for the first time, providing a two-step access to virtually enantiopure N-protected beta-amino acids.     

The rearrangement of 4-hydroxyeoumarin carbamates

Carbamate esters of 4-hydroxycoumarin were prepared, and their base-catalyzed and thermal rearrangement to 3-(N-substituted carbamoy])-4-hydroxycoumarins were studied. A mechanism for the rearrangement is proposed.     

Prenyl carbamates: preparation and deprotection

Prenyloxycarbonylimidazole (PreocIm) and prenyl p-nitrophenyl carbonate (PreocOC₆H₄p-NO₂), two substitutes for the unstable prenyl chloroformate, allowed an efficient introduction of the prenyloxycarbonyl group to a variety of primary and secondary amines. Deprotection of prenyl carbamates was readily achieved by, first their conversion to 2-iodo-3-methoxy-3-methylbutyl carbamates with iodine in methanol followed by reductive β-elimination with zinc powder. These reaction conditions are compatible with the presence of a number of functional groups such as Boc and Cbz carbamates, sulfides, double bonds, indoles and aromatic ethers.     

Intersequence cyclization in copolymers of N-vinyl carbamates

Monomer reactivity ratios determined for the copolymerization of tert-butyl N-vinylcarbamate (r_A = 0.55 ± 0.05) with phenyl N-vinylcarbamate (r_B = 2.08 ± 0.15) indicate that the monomer units are distributed randomly along the polymer chains. The following sequence of reactions was used to cause intersequence cyclization between tert-butyl N-vinylcarbamate and phenyl N-vinylcarbamate units in the copolymers. The extent of cyclization obtained was in accord with that expected for random copolymers.      

Phenanthroline complexes of zinc and calcium carbamates

Bis(N,N‐di‐n‐butyl­di­thio­carbamato‐κ²S,S′)(1,10‐phenanthroline‐κ²N,N′)­zinc(II) ethanol hemisolvate, [Zn(C₉H₁₈NS₂)₂(C₁₂H₈N₂)]·0.5C₂H₆O, (I), and bis(N,N‐di‐n‐hexyldithiocarbamato‐κ²S,S′)­bis(1,10‐phenanthroline‐κ²N,N′)calcium(II), [Ca(C₁₃H₂₆NS₂)₂(C₁₂H₈N₂)₂], (II), are mixed‐ligand com­plexes. In the first compound, the Zn atom has a distorted octahedral coordination, while in the second compound, the Ca atom is eight‐coordinate, with four S and four N atoms forming a highly distorted cube.     

Dye sensitized photooxygenation of substitute oxime carbamates

Sojvolytic cleavage of oxime carbamates can be achieved by dye sensitized photooxygenation. A study with substituted oxime carbamates has revealed an unusual chemoselectivity of singlet oxygen towards carbon—nitrogen single bonds in preference over carbon—nitrogen double bonds in such compounds.     

Copper-catalyzed tethered aziridination of unsaturated N-tosyloxy carbamates

Aziridines were formed by copper-catalyzed intramolecular nitrene addition to alkenes. The carbamate group was used as the tether between the alkene and the nitrene. Subsequent nucleophilic attack of the aziridine was accomplished using RSH, R2NH, N3-, or ROH as the nucleophile. This addition was found to be regio- and stereoselective. This methodology has been used to demonstrate its utility in the regio- and stereoselective synthesis of a 1,2-diamino-3-hydroxycyclohexane. This substitution pattern is found in natural products such as Tamiflu.