Synthesis of imidazolidin-2-one-4-carboxylate and of (tetrahydro)pyrimidin-2-one-5-carboxylate via an efficient modification of the Hofmann rearrangement

A mild and efficient methodology for the rearrangement of protected asparagine and protected glutamine is reported; good results are obtained with a wide selection of protecting groups.     

Synthesis of orthogonally protected (R)- and (S)-2-methylcysteine via an enzymatic desymmeterization and Curtius rearrangement

A synthesis of differentially protected (R)- and (S)-2-methylcysteines is described. Monomethylation of dimethylmalonate followed by alkylation with tert-butylchloromethyl sulfide gave an achiral diester. Desymmeterization by selective hydrolysis of one ester with pig-liver esterase gave the acid in 97% chemical yield and 91% enantiomeric excess. Heating this acid with diphenylphosphoryl azide followed by 4-methoxybenzyl alcohol gave protected (R)-2-methylcysteine. Alternately, the acid and ester groups were interchanged and heated with diphenylphosphoryl azide followed by 4-methoxybenzyl alcohol, giving protected (S)-2-methylcysteine.     

A simple and efficient procedure for the synthesis of benzimidazoles using trichloroisocyanuric acid (TCCA) as the oxidant

A Direct one step synthesis of various benzimidazoles from 3,4‐diaminotoluene and benzaldehydes is described using TCCA as the oxidant. The salient features of this method include simple procedure, mild condition, no waste products, easy separation, low reaction times and generality.     

3-Aminopyrrolidines via ring rearrangement of 2-aminomethylazetidines. Synthesis of (-)-absouline

[reaction: see text] A new entry to enantiopure 3-aminopyrrolidines was developed using a boron trifluoride-mediated rearrangement of 2-aminomethylazetidines. The method is quite general and produces rearranged products in good yield regardless of both substitution pattern and relative stereochemistry of the starting material. A concise stereocontrolled synthesis of (-)-absouline was achieved on the basis of this new method.     

1-Phenylthio-1-(trimethylsiloxy)cyclopropanes via the sila-Pummerer rearrangement

This first study of the sila-Pummerer rearrangement in a cyclopropane system reveals that several 1-trimethylsiloxy-1 -(phenylthio)cyclopropanes can be prepared stereoselectively through putative sulfur-stabilized carbocationic intermediates.     

Synthesis of 1-arylmethyl-2-(2-cyanoethyl)aziridines and their rearrangement into novel 2-(aminomethyl)cyclopropanecarbonitriles

1-Arylmethyl-2-(bromomethyl)aziridines were transformed into novel 2-(2-cyanoethyl)aziridines upon treatment with alpha-lithiated trimethylsilylacetonitrile in THF in an efficient and straightforward approach. The latter aziridines underwent ring opening by reaction with benzyl bromide in acetonitrile, affording 5-amino-4-bromopentanenitriles through a regiospecific ring opening of intermediate aziridinium salts by bromide. Further elaboration of these gamma-bromonitriles resulted in the synthesis of novel 2-[N,N-bis(arylmethyl)aminomethyl]cyclopropanecarbonitriles in high yields by means of a 1,3-cyclization protocol upon treatment with KOtBu in THF.     

Studies on the sequential claisen rearrangement of methyl-3-arlyloxy- 2-(aryloymethyl)prop-2-enolates

Claisen rearrangement of methyl-3-aryloxy-2-(aryloxymethyl)prop-2-enoates (4) in refluxing N,N-diethylaniline gave 3-(2-hydroxyphenylmethylene) -3,4-dihydro-2H-1-benzopyran-2-ones (6) and 3-methoxycarbonyl-2H-1-benzopyrans(7).     

Synthesis of 2-(2-selenienyl)pyrrole from methyl-2-selenienylketoxime and acetylene

The reaction of methyl-2-selenienylketoxime with acetylene in KOH-DMSO gives 2-(2-selenienyl)pyrrole and its 1-vinyl derivative.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 708–710, May, 1992.     

Functionalisation of 1,2,3-triazole via lithiation of 1-[2-(trimethylsilyl)ethoxy]methyl-1H-1,2,3-triazole

The preparation of a number of 5-substituted 1-[2-(trimethylsilyl)ethoxy]methyl-1H-1,2,3-triazoles via reaction of 1-[2-(trimethylsilyl)ethoxy]methyl-1H-1,2,3-triazole with n-butyllithium followed by addition of various electrophiles is reported. Removal of the protecting group by action of diluted aqueous hydrochloric acid or by tetrabutylammonium fluoride in tetrahydrofuran leads to the appropriate 4-substituted 1H-1,2,3-triazoles.     

Efficient synthesis of methyl carbamate via Hofmann rearrangement in the presence of TsNBr2

An efficient method has been developed for the synthesis of carbamates from the corresponding amides via the Hofmann rearrangement using N,N-dibromo-p-toluenesulfonamide (TsNBr₂) in the presence of DBU in methanol. The reaction goes into completion in 10–20 min at 65 °C to produce the corresponding carbamate in excellent yield.     

2-苯羟甲基-5,5-二甲基-4-苯基-2-氧代1,3,2-二氧磷杂环己烷的合成及表征

以苯甲醛、异丁醛、三氯化磷为原料合成了新型的1,3,2-二氧磷杂环类化合物2-苯羟甲基-5,5-二甲基-4-苯基-2-氧代-1,3,2-二氧磷杂环己烷,总收率为40．8％,并对其进行了NMR研究和结构表征。     

Synthesis of aliphatic isocyanates via a two-phase Hofmann reaction

A convenient method of preparing aliphatic isocyanates via a two-phase Hofmann reaction using a phase transfer catalyst is described.     

Synthesis of (R)-2-(benzyloxy)-tetrahydro-5,5-dimethylfuran by a new oxidative rearrangement

The rearrangement under oxidative conditions of 3-(benzyloxy)-tetrahydro- 2,6,6-trimethyl-2H-pyran-2-carbaldehydes to afford a chiral protected tetrahydrofuran lactol is described.     

Synthesis and herbicidal activities of methyl-1-(2,4-dichlorophenoxyacetoxy)alkylphosphonate monosalts

A series of 1-(2,4-dichlorophenoxyacetoxy)alkylphosphonic acid dimethyl esters 5 and its corresponding phosphonate monosalts 6 were synthesized as potential herbicide. The phosphonate monosalts can be prepared from 1-(2,4-dichlorophenoxyacetoxy)alkylphosphonic acid dimethyl esters 5, which were synthesized by the condensation of O,O-dimethyl-1-hydroxyalkylphosphonates with dichlorophenoxyacetic chloride. This method provides a simple and efficient procedure for the synthesis of phosphonate derivatives containing sensitive groups to acid, base or water such as carboxylate ester bond; and the herbicidal activity of title compounds was evaluated in a set of experiments in greenhouse. Most of the compounds exhibited notable herbicidal activity.     

Entering the leinamycin rearrangement via 2-(trimethylsilyl)ethyl sulfoxides

Attack of cellular thiols on the antitumor natural product leinamycin is believed to generate a sulfenate intermediate that undergoes subsequent rearrangement to a DNA-alkylating episulfonium ion. Here, 2-(trimethylsilyl)ethyl sulfoxides were employed in a fluoride-triggered generation of sulfenate anions related to the putative leinamycin-sulfenate. The resulting sulfenates enter smoothly into a leinamycin-type rearrangement reaction to afford an episulfonium ion alkylating agent. The results provide evidence that the sulfenate ion is, indeed, a competent intermediate in the leinamycin rearrangement. Further, the molecules examined here may provide a foundation for the design of functional leinamycin analogues that bypass the unstable and synthetically challenging 1,2-dithiolan-3-one 1-oxide moiety found in the natural product.     

Synthesis of 2-(methoxycarbonyl)methyl-7-phenylacetamido-3-thiacepham-4-carboxylates

Representatives of the title compounds have been prepared from a benzyl-penicillin-derived intermediate.     

A highly enantioselective phase-transfer catalyzed epoxidation of enones with a mild oxidant, trichloroisocyanuric acid

The enantioselective epoxidation can be carried out using trichloroisocyanuric acid (TCCA) as oxidant in the presence of chiral quaternary ammonium salt as a phase-transfer catalyst; treatment of chalcone derivatives with TCCA under mild conditions afforded the corresponding epoxy ketones in good yields with moderate to excellent enantioselectivities of up to 96%.     

1-Methoxy-1-(phenylthio)cyclopropanes from olefins via the Pummerer rearrangement

The Pummerer rearrangements of cyclopropyl(methoxy)phenylsulfonium salts proceed via sulfur-stabilized carbocations to yield the title compounds. The sulfonium salts were prepared in high yields from olefins via carbene addition, oxidation, and methylation.