Stereoselective alkoxycarbonylation of unactivated C(sp^3)–H bonds with alkyl chloroformates via Pd(II)/Pd(IV) catalysis

Several examples on Pd-catalysed carbonylation of methyl C(sp^3)–H bonds with gaseous CO via Pd(II)/Pd(0) catalysis have been reported. However, methylene C(sp^3)–H carbonylation remains a great challenge, largely due to the lack of reactivity of C–H bonds and the difficulty in CO migratory insertion. Herein, we report the stereoselective alkoxycarbonylation of both methyl and methylene C(sp^3)–H bonds with alkyl chloroformates through a Pd(II)/Pd(IV) catalytic cycle. A broad range of aliphatic carboxamides and alkyl chloroformates are compatible with this protocol. In addition, this process is scalable and the directing group could be easily removed under mild conditions with complete retention of configuration

Kinetics and Mechanism of Hydrolysis of Benzimidazolylcarbamates

Synthesis of new 2-aminobenzimidazole-1-carbamates was accomplished by carbamoylation of 2-aminobenzimidazole using different substituted phenyl chloroformates. The aqueous hydrolysis of the new compounds was examined in the pH range 1-13 at 25 oC. The evaluated kinetic parameters led to the conclusion that up to pH 4 reaction proceeds by a bimolecular attack of water to the N-protonated substrate. This is the first time this behavior is described for carbamates, and can be ascribed to the higher basicity of the benzimidazolyl moiety when compared with the carbonyl oxygen. For higher values of pH, the results are consistent with a BAc2 mechanism with nucleophilic catalysis, but while between pH 4 and pH 7 water acts as the nucleophile, for pH> 7 the hydroxide ion is the acting species

Asymmetric addition of chiral boron-ate complexes to cyclic iminium ions

Boron-ate complexes derived from enantioenriched secondary benzylic boronic esters and aryl lithiums have been reacted with quinolinium, pyridinium and dihydroisoquinolinium salts to give enantioenriched heterocyclic structures with very high diastereocontrol over two contiguous stereogenic centres (87: 1 3-99 : 1 dr; &gt;95 : 5 es). The salts were derived from the corresponding heterocycle and Troc-Cl or dimethylTroc-Cl. In the case of the quinolinium and pyridinium salts, the presence of a 3-carboxyamide group increased both reactivity and diastereoselectivity. The unusually high diastereoselectivity observed is thought to originate from strong cation-p interactions between the cationic heterocycle and the electron rich benzylic boronate complex with minimisation of steric interactions between the substituents on the ate complex and the non-planar substituents on the heterocycle.</p

One-pot domino synthesis of polyvicinalamine monomers

On a genere de l'imidazole par une reaction de type domino in situ entre le glyoxal, le formaldehyde et deux unites d'ammoniac aqueux. L'addition de bicarbonate aqueux et d'un anhydride carboxylique ou d'un dicarbonate de dialkyle conduit a la formation de la N,N'-diacyl- ou N,N'-dicarbalkoxy-2-hydroxyimidazoline correspondante. Il s'ensuit une reaction de clivage de cycle de Bamberger qui permet d'isoler facilement le cis-1,2-di(acetamido)ethene, le cis-1,2-di(propylamido)ethene, le cis-1,2-di(ethoxyamido)ethene, le cis-1,2-di(tert-butoxyamido)ethene ou le cis-1,2-di(benzamido)ethene sous la forme de solides. La facilite et la generalite offerte par cette approche monotope implique une voie efficace du point de vue des couts en vue de la synthese de routine de precurseurs d'amines oligo- et polyvicinales

One pot domino synthesis of polyvicinalamine monomers

On a genere de l'imidazole par une reaction de type domino in situ entre le glyoxal, le formaldehyde et deux unites d'ammoniac aqueux. L'addition de bicarbonate aqueux et d'un anhydride carboxylique ou d'un dicarbonate de dialkyle conduit a la formation de la N,N'-diacyl- ou N,N'-dicarbalkoxy-2-hydroxyimidazoline correspondante. Il s'ensuit une reaction de clivage de cycle de Bamberger qui permet d'isoler facilement le cis-1,2-di(acetamido)ethene, le cis-1,2-di(propylamido)ethene, le cis-1,2-di(ethoxyamido)ethene, le cis-1,2-di(tert-butoxyamido)ethene ou le cis-1,2-di(benzamido)ethene sous la forme de solides. La facilite et la generalite offerte par cette approche monotope implique une voie efficace du point de vue des couts en vue de la synthese de routine de precurseurs d'amines oligo- et polyvicinales

Reaction of carboxylic dyes with wool and polyamide. Part III: Effect of the activating agent

Dyes containing a carboxylic acid group had been shown to react with wool and polyamide fibres when activated with ethyl chloroformate (Parts I and II). One of the dyes, 3-aminobenzoic acid →N,N-dimethylaniline, was, in this work, activated with other chlorofirmates, so as to improve the dyeing conditions. Benzyl chloroformate was found to be a good substitute since it is not as volatile as ethyl chloroformate, which suggests that it will be easier to apply in practical dyeing conditions. The yield of the reaction with cyclohexylamine is similar to the one obtained with ethyl chloroformate, suggesting that the fixation of the dye on wool or polyamide will be much the same. The fastness results are also equivalent.FCT-Fundação para a Ciência e Tecnologi

A practical route to tertiary diarylmethylamides or -carbamates from imines, organozinc reagents and acyl chlorides or chloroformates

A practical route to tertiary diarylmethylamides or -carbamates from imines, organozinc reagents and acyl chlorides or chloroformates is described. This route involves the formation of an imine, which is used without isolation, followed by its activation by the carbonyl-containing electrophile and the trapping of the acyliminium by an organozinc reagent. Most steps are conducted concomitantly to render the procedure as practical and straightforward as possible. Therefore, the whole experimental protocol takes less than two hours

Fmoc-2-Mercaptobenzothiazole (MBT), for the Introduction of the Fmoc Moiety Free of Side-Reactions

A double side-reaction, consisting in the formation of Fmoc--Ala-OH and Fmoc--Ala-AA-OH, during the preparation of Fmoc protected amino acids (Fmoc-AA-OH) with Fmoc-OSu is discussed. Furthermore, the new Fmoc-2-MBT reagent is proposed for avoiding these side-reactions as well as the formation of the Fmoc-dipeptides (Fmoc-AA-AA-OH) and even tripeptides, which is another important side-reaction when chloroformates such as Fmoc-Cl is used for the protection of the -amino function of the amino acids

Chemical profile of the organic residue from ancient amphora found in the Adriatic Sea determined by direct GC and GC-MS analysis

An ancient organic residue was collected from the bottom of a Greco-Italian amphora found in the Adriatic Sea and investigated by direct GC and GC- MS analysis. The headspace composition was determined by HS-SPME using: (1) DVB/CAR/PDMS and (2) PDMS/DVB fibres. Higher percentages of benzene derivatives, monoterpenes and other low- molecular aliphatic compounds were obtained by method (1) in contrast to higher percentage of naphthalene and phenanthrene derivatives found by method (2). In comparison with the composition of pine resin, it is more likely that the found low- molecular aliphatic alcohols, acids, esters and carbonyls with 2-phenylethanol were trapped and preserved within the organic residue from stored wine – the amphora’s originally content. Semi- volatile diterpenes methyl dehydroabietate (33.6%) and retene (24.1%) were dominant in the residue CH2Cl2 solution. Other abundant compounds were 1, 4-dimethoxyphenanthrene (6.8%) as well as other naphthalene and/or phenanthrene derivatives [7-(1- methylethyl)-1, 4a-dimethyl-1, 2, 3, 4, 4a, 9, 10, 10a- octahydronaphthalene, 7-(1-methylethyl)-1, 4a- dimethyl-2, 3, 4, 4a, 9, 10-hexahydrophenanthrene, 7- (1-methylethyl)-1, 4a-dimethyl-1, 2, 3, 4, 4a, 9, 10, 10a- octahydro-phenanthrene, 3, 6-dimethylphenanthrene and 2, 3, 5-trimethylphenanthrene]. Possible sources and formation pathways of the major compounds in the residue were discussed