A general, practical, and efficient method for the dimerization of dithiocarbamates has been developed that can be used to prepare the corresponding bis(1-arylimino-1-alkyl/arylthiomethyl) disulfides with dilauroyl peroxide (DLP) as mild oxidant. Notably, a lauroyl radical, rather than an undecyl radical, was established as the radical hydrogen-abstractor during the dimerization process. The amount of DLP impacts the dimerization yield, with 50 mol-% DLP giving the disulfides in the highest yields. The use of an excess of DLP generates the undecyl radical, which decomposes the disulfides rapidly to the corresponding isothiocyanates.

A series of β-ketonitriles was synthesized within 30 min under mild conditions through the BF₃·OEt₂-catalyzed addition reactions of diazoacetonitrile to aromatic aldehydes and subsequent 1,2-hydride shift. This method is advantageous in that it is operationally simple, mild and metal-free conditions are used, the substrate scope is wide, and the products are obtained in moderate to high yields (up to 81 %). Additionally, γ,δ-unsaturated β-ketonitriles are also accessible by this method by using cinnamaldehydes.

An economical, practical, and green protocol with which to synthesize 3-alkylideneoxindoles from α-diazo-β-ketoanilides has been developed. The approach employs inexpensive Cu(NO₃)₂·3H₂O as catalyst and environmentally friendly water as solvent, and achieves moderate to excellent yields. The method has good tolerance to a range of N-alkyl and N-aryl groups, including electron-withdrawing and electron-donating groups on the aromatic ring, ortho-, meta-, and para-substituents, and β-aliphatic and β-aromatic keto groups. A plausible mechanism involving intramolecular aromatic metal carbene electrophilic addition as the key step is proposed.

A series of new C₂-symmetric (1S,2S)-cyclohexane-1,2-dicarboxamides was synthesized from (1S,2S)-cyclohexane-1,2-dicarbonyl dichloride and N-benzyl-substituted aromatic amines, which were prepared from 2-aminopyridine, 2-chloroaniline, and 2-aminophenol via imine formation with benzaldehyde and subsequent reduction with NaBH₄. (1S,2S)-N,N′-Dibenzyl-N,N′-bis[2-(benzyloxy)phenyl]cyclohexane-1,2-dicarboxamide was converted to (1S,2S)-N,N′-dibenzyl-N,N′-bis(2-hydroxyphenyl)cyclohexane-1,2-dicarboxamide via hydrogenolysis in the presence of Pd(OH)₂ on active carbon powder.

An enantioselective Michael addition of thioacetic acid (AcSH) to nitroalkenes, catalyzed by a leucine-derived bifunctional aminethiourea, was developed with high yields and moderate enantioselectivities. The thiourea-ammonium salt formed in the reaction is identified as the active catalyst, and the multiple H-bonding system is responsible for the stereocontrol. The resulting thioester products are useful intermediates for the synthesis of enantiomerically enriched S-containing compounds.

A chemospecific intramolecular Buchner reaction of N-benzyl-2-cyano-2-diazoacetamides catalyzed by inexpensive copper(II) acetylacetonate (acac) has been achieved to synthesize a variety of 9-aza-1-cyanobicyclo[5.3.0]deca-2,4,6-trien-10-ones, 5,7-bicyclic products. The methodology involves sole chemoselectivity, an inexpensive metal catalyst, broad substrate scope, and moderate to excellent yields.

The chemoselectivity in the reaction of 2-diazo-3-oxo-3-phenylpropanal (1) with aldehydes and ketones in the presence of Et₃N was investigated. The results indicate that 1 reacts with aromatic aldehydes with weak electron-donating substituents and cyclic ketones under formation of 6-phenyl-4H-1,3-dioxin-4-one derivatives. However, it reacts with aromatic aldehydes with electron-withdrawing substituents to yield 1,3-diaryl-3-hydroxypropan-1-ones, accompanied by chalcone derivatives in some cases. It did not react with linear ketones, aliphatic aldehydes, and aromatic aldehydes with strong electron-donating substituents. A mechanism for the formation of 1,3-diaryl-3-hydroxypropan-1-ones and chalcone derivatives is proposed. We also tried to react 1 with other unsaturated compounds, including various olefins and nitriles, and cumulated unsaturated compounds, such as N,N′-dialkylcarbodiimines, phenyl isocyanate, isothiocyanate, and CS₂. Only with N,N′-dialkylcarbodiimines, the expected cycloaddition took place.

Various substituted homotaurines (=3-aminopropane-1-sulfonic acids) 6 were readily synthesized in satisfactory to good yields via the Michael addition of thioacetic acid to alk-2-enamides 3 (4), followed by LiAlH₄ reduction (5) and performic acid oxidation (Scheme 1). The configuration of ‘anti’-disubstituted homotaurine ‘anti’-6h was deduced from the 3-(acetylthio)alkanamide (=S-(3-amino-1,2-dimethyl-3-oxopropyl) ethanethioate)‘anti’-4h formed in the Michael addition, which was identified via the Karplus equation analysis, and confirmed by X-ray diffraction analysis. The current route is an efficient method to synthesize diverse substituted homotaurines, including 1-, 2-, and N-monosubstituted, as well as 1,2-, 1,N-, 2,N-, and N,N-disubstituted homotaurines (Table).

The cycloaddition of ketenes and imines (Staudinger cycloaddition) is a general method for the synthesis of various β-lactams. However, reactions of imines and ketenes with electron-withdrawing substituents produce α,β-unsaturated alkenamides, ring-opening products of the intermediates generated from imines and the ketenes, even as sole products, besides the desired β-lactams. The mechanism of the formation of α,β-unsaturated alkenamides was investigated. The results indicate that the α,β-unsaturated alkenamides are generated via a base-induced CC bond isomerization followed by electrocyclic ring opening of the formed azacyclobutenes (=1,2-dihydroazetes; cf. Scheme 3).

Taurine and structurally diverse substituted taurines have been synthesized by peroxyformic acid oxidation of the thiazolidine-2-thione intermediates generated from vicinal amino alcohols or aziridines and carbon disulfide. Thestereochemistry and mechanisms of the reactions are disscussed. The method is a salt-free and versatile route, convenient in terms of purification, and can be used to synthesize optically active substituted taurines. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

An effective and versatile method was developed to synthesize N-benzyloxycarbonyl-protected and free 2,2-disubstituted taurines. Several novel 2,2-disubstituted taurines, including aliphatic/aromatic and cyclic/acyclic derivatives, were obtained, which demonstrates the generality of this method. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)