How easy are the syntheses of allenes

Use of Lawesson's reagent in organic syntheses.

Bromination is one of the most important transformations in organic synthesis and can be carried out using bromine and many other bromo compounds. Use of molecular bromine in organic synthesis is well-known. However, due to the hazardous nature of bromine, enormous growth has been witnessed in the past several decades for the development of solid bromine carriers. This review outlines the use of bromine and different bromo-organic compounds in organic synthesis. The applications of bromine, a total of 107 bromo-organic compounds, 11 other brominating agents, and a few natural bromine sources were incorporated. The scope of these reagents for various organic transformations such as bromination, cohalogenation, oxidation, cyclization, ring-opening reactions, substitution, rearrangement, hydrolysis, catalysis, etc. has been described briefly to highlight important aspects of the bromo-organic compounds in organic synthesis.

Use of Bromine and Bromo-Organic Compounds in Organic Synthesis

Garlic has long been considered as a natural remedy against a range of human illnesses, including various bacterial, viral and fungal infections. This kind of antibiotic activity of garlic has mostly been associated with the thiosulfinate allicin. Even so, recent studies have pointed towards a significant biological activity of trisulfides and tetrasulfides found in various Allium species, including a wide range of antibiotic properties and the ability of polysulfides to cause the death of certain cancer cells. The chemistry underlying the biological activity of these polysulfides is currently emerging. It seems to include a combination of several distinct transformations, such as oxidation reactions, superoxide radical and peroxide generation, decomposition with release of highly electrophilic Sx species, inhibition of metalloenzymes, disturbance of metal homeostasis and membrane integrity and interference with different cellular signalling pathways. Further research in this area is required to provide a better understanding of polysulfide reactions within a biochemical context. This knowledge may ultimately form the basis for the development of ‘green’ antibiotics, fungicides and possibly anticancer agents with dramatically reduced side effects in humans.

Polysulfides as biologically active ingredients of garlic

III. Structures of Organic Polysulfanes 3922 A. General 3922 B. Structures of Chain-Like R−Sn−R Molecules 3923 C. Structures of Cyclic R−Sn−R Molecules 3924 D. Conformational Studies 3925 IV. Analysis of Organic Polysulfanes 3925 A. General 3925 B. NMR Spectroscopy 3926 C. Chromatography 3926 D. Raman Spectroscopy 3928 E. XANES Spectroscopy 3928 V. Reactions of Organic Polysulfanes 3928 A. Interconversion Reactions 3928 B. Sulfur Transfer Reactions 3930 C. Replacement Reactions 3931 D. Nucleophilic Displacement Reactions at the Sulfur−Sulfur Bond 3931

The chemistry of organic polysulfanes R-Sn-R (n > 2)

3,5-Disubstituted 1,2,4-thiadiazoles 2 were prepared by reaction of thioamides 1 with DMSO in the presence of such an electrophilic reagent as 1-methyl-2-chloropyridinium iodide, benzoyl chloride, acetyl chloride, hydrochloric acid, or trimethylsilyl chloride in organic solvents at room temperature in high yields. Thiadiazoles 2 were also obtained by reaction of 1 with NBS at room temperature in high yields. Thioamide S-oxides reacted with electrophilic reagents at room temperature to give the corresponding thiadiazoles 2 in high yields.

Convenient Preparations of 3,5-Disubstituted 1,2,4-Thiadiazoles by Oxidative Dimerization of Thioamides

Effects of molecular structure of aliphatic diols and polyalkylene glycol as lubricants on the wear of aluminum

Novel synthesis of 1,3,5-triselenanes from aldehydes, and novel generation of selenoaldehydes by fragmentation of 1,3,5-triselenanes

The reactions of amides and N,N,N′,N′-tetramethylurea with (Me3Si)2Se in the presence of BF3·OEt2 afforded the corresponding slelenoxo compounds in good yields. On the other hand, selenation of ethyl and butyl benzoates in a similar manner gave benzoin and 2,3,5,6-tetraphenyl-1,4-diselenin via selenoesters. The trapping of selenoesters was also achieved by 2,3-dimethyl-1,3-butadiene to afford [4+2] cycloadducts.

Conversion of amides, N,N,N',N'-tetramethylurea, and esters to the corresponding selenoxo compounds by treatment with bis(trimethylsilyl) selenide and BF3.OEt2

Selenoaldehydes and selenoketones were generated in situ, by treating aldehydes or ketones, respectively, with bis(1,5-cyclooctanediylboryl) selenide; the resulting selenocarbonyl compounds were trapped with 2,3-dimethyl-1,3-butadiene to give the corresponding [4+2] cycloadducts. The treatment of amides, an ester, and ketones possessing bulky substituents with the reagent also afforded the corresponding selenoamides, a selenoester, and sterically protected selones, respectively, in modest yields. On the other hand, a similar treatment of cinnamaldehyde with the reagent gave the 2,3-dihydroselenophene derivative, which originated from a [4+2]-type self-dimerization of in situ generated 3-phenyl-2-propeneselenal.

Yuji Takikawa

Papers

Convenient Preparations of 3,5-Disubstituted 1,2,4-Thiadiazoles by Oxidative Dimerization of Thioamides

Effects of molecular structure of aliphatic diols and polyalkylene glycol as lubricants on the wear of aluminum

Novel synthesis of 1,3,5-triselenanes from aldehydes, and novel generation of selenoaldehydes by fragmentation of 1,3,5-triselenanes

Conversion of amides, N,N,N',N'-tetramethylurea, and esters to the corresponding selenoxo compounds by treatment with bis(trimethylsilyl) selenide and BF3.OEt2

Efficient Synthesis of Selenocarbonyl Compounds by Treating Carbonyl Compounds with Bis(1,5-cyclooctanediylboryl) Selenide