Enantiospecific Synthesis of Swainsonine, (1S, 2R, 8R, 8aR)-1,2,8-trihydroxyoctahydroindolizine,from D-mannose

An enantiospecific synthesis of swainsonine from D-mannose is described; the heterocyclic rings of swainsonine are constructed by two intramolecular reductive aminations caused by the catalytic hydrogenation of an azidoaldehyde with 5 equivalents of hydrogen.     

Dimeres N-Lithium-N′,N′-bis(dimethylphenylsilyl)- und trimeres N,N′-Dilithium-N,N′-bis(dimethylphenylsilyl)hydrazid – Synthesen,Strukturen und Reaktionen

Dimeric N-Lithium-N′,N′-bis(dimethyphenylsilyl)- and trimeric N,N′-Dilithium-N,N′-bis(dimethylphenylsilyl)hydrazide – Syntheses, Structures, and Reactions Dilithiated hydrazine reacts with two equivalents chlorodimethylphenylsilane to the isomeric bis(silyl)hydrazines 1 a and 1 b . Reactions of 1 a / 1 b with one and two equivalents n-butyllithium lead to the lithium derivatives 2 and 4 . The crystal structure analyses of 2 and 4 are reported. 2 forms with difluorodiisopropylsilane the tris(silyl)hydrazine 3 . The tetrakis(silyl)hydrazines 5 and 6 are formed in reactions of 4 with trifluoromethylsilane and tetrafluorosilane.     

Intramolecular, reductive cyclization of beta-ketoisothiocyanates promoted by using samarium diiodide

A novel samarium diiodide (SmI2) promoted intramolecular cyclization of beta-ketoisothiocyanate, derived from alpha,beta-unsaturated esters and ammonium thiocyanate led to alpha-hydroxythiolactams and/or thiolactams in high yields. Treatment of beta-ketoisothiocyanate with two equivalents of SmI2 gave a mixture of alpha-hydroxythiolactam and thiolactam. Four equivalents of SmI2 afforded only thiolactam in high yields. The intramolecular cyclization took place with high to complete stereoselectivity. A mechanism to explain this transformation is proposed.     

Unusual product from the acid-catalyzed one-pot,multicomponent reaction of thiocarbohydrazide,aldehydes, and phenacyl bromides

A one-pot, three-component protocol for the synthesis of novel five-membered thiazole ring bonded to two hydrazone motifs is described. The acid-catalyzed reaction of one equivalent of thiocarbohydrazide, two equivalents of aromatic aldehydes, and one equivalent of phenacyl bromides afforded the five-membered thiazole ring. The reactions proceed with novel chemoselectivity. Similar reported protocols have always afforded 1,3,4-thiadiazines.     

Alkali and alkaline-earth metal ketyl complexes: isolation, structural diversity, and hydrogenation/protonation reactions

The use of hexamethylphosphoric triamide (HMPA) as a stabilizing ligand allowed successful isolation of a series of structurally characterizable alkali metal and calcium ketyl complexes. Reaction of lithium and sodium with one equivalent of fluorenone and reaction of sodium with one equivalent of benzophenone in THF, followed by addition of two equivalents of HMPA, yielded the corresponding ketyl complexes 1, 2, and 11, respectively, as microketyl-bridged dimers. If one equivalent of HMPA was used in the reaction of sodium with fluorenone, a further aggregated complex, the mu3-ketyl-bridged tetramer 3, was isolated, whereas analogous reaction of benzophenone with sodium afforded the trimeric ketyl complex 13, rather than a simple benzophenone analogue of 3. In the reaction of potassium with fluorenone, the use of two equivalents of HMPA gave the tetramer 4, rather than a dimeric complex analogous to 1 or 2. Compared to the tetrameric sodium complex 3, there is an extra HMPA ligand that bridges two of the four K atoms in 4. When 0.5 equiv of HMPA was used in the above reaction, complex 5, a THF-bridged analogue of 4, was isolated. In the absence of HMPA, the reaction of sodium with an excess of fluorenone yielded the tetrameric ketyl complex 6, in which two of the four Na atoms are each terminally coordinated by a fluorenone ligand, and the other two Na atoms are coordinated by a THF ligand. Two bridging THF ligands are also observed in 6. Reaction of 1,2-bis(biphenyl-2,2'-diyl)ethane-1,2-diol (7) with two equivalents of LiN(SiMe3)2 or NaN(SiMe3)2 in the presence of four equivalents of HMPA easily afforded 1 or 2, respectively, via C-C bond cleavage of a 1,2-diolate intermediate. The reaction of calcium with two equivalents of fluorenone or benzophenone in the presence of HMPA gave the corresponding complexes that bear two independent ketyl ligands per metal ion. In the presence of 3 or four equivalents of HMPA, the fluorenone ketyl complex was isolated in a six-coordinate octahedral form (10), while the benzophenone ketyl complex was obtained as a five-coordinate trigonal bipyramid (13). The radical carbon atoms in both benzophenone ketyl and fluorenone ketyl complexes are still in an sp2-hybrid state. However, in contrast with the planar configuration of the whole fluorenone ketyl unit, the radical carbon atom in a benzophenone ketyl species is not coplanar with any of the phenyl groups; this explains why benzophenone ketyl is more reactive than fluorenone ketyl. Hydrolysis of 2 or 11 with 2N HCI yielded the corresponding pinacol-coupling product, while treatment of 2 or 11 with 2-propanol, followed by hydrolysis, gave the pairs fluorenone and fluorenol or benzophenone and benzhydrol, respectively. A possible mechanism for these reactions is proposed.     

相转移催化合成O,O-二芳基(硫代)磷酰氯

用０．０５ｍｏｌ三氯硫磷和０．１０ｍｏｌ的酚通过相转移催化反应合成Ｏ,Ｏ-二芳氧基硫代磷酸氯可得较好收率。产物经ＩＲ和１ＨＮＭＲ表征。     

H2-release from alcohols,diols, and compounds with amino functionality promoted by titanium(II) sandwich complex, [Cp2Ti]: a theoretical approach

Structural Chemistry - The role of Ti(II) sandwich complex, [Cp2Ti], generated by the combination of [Cp2TiCl2] and two equivalents of nBuLi, in situ, in toluene has been investigated theoretically...     

Click 1,4-regioselective synthesis,characterization, and antimicrobial screening of novel 1,2,3-triazoles tethering fluorinated 1,2,4-triazole and lipophilic side chain

Research on Chemical Intermediates - Base-catalyzed alkylation of 5-(4-fluorophenyl)-2,4-dihydro-1,2,4-triazole-3-thione (3) with one or two equivalents of propargyl bromide in presence of...     

Dianionic Tris[oxalato(2—)]silicate and Tris[oxalato(2—)]germanate Complexes: Synthesis,Properties, and Structural Characterization in the Solid State and in Solution

Reaction of tetramethoxysilane with three molar equivalents of oxalic acid and two molar equivalents of 1‐(2‐hydroxyethyl)‐pyrrolidine or 1‐(2‐hydroxyethyl)piperidine in tetrahydrofuran yielded the λ⁶Si‐silicates 1‐(2‐hydroxyethyl)pyrrolidinium tris[oxalato(2—)]silicate ( 4 ) and 1‐(2‐hydroxyethyl)piperidinium tris[oxalato(2—)]silicate ( 5 ). The related germanium compounds 1‐(2‐hydroxyethyl)piperidinium tris[oxalato(2—)]germanate ( 6 ) and triethylammonium tris[oxalato(2—)]germanate ( 7 ) were synthesized analogously, starting from tetramethoxygermane and using three molar equivalents of oxalic acid and two molar equivalents of 1‐(2‐hydroxyethyl)piperidine or triethylamine. Compounds 4 — 7 were characterized by elemental analyses (C, H, N), single‐crystal X‐ray diffraction, solid‐state VACP/MAS NMR spectroscopy (²⁹Si), and solution NMR spectroscopy (¹H, ¹³C, ²⁹Si). The structural characterization was complemented by computational studies of the tris[oxalato(2—)]silicate dianion and the tris[oxalato(2—)]germanate dianion. In addition, the stability of compounds 4 — 7 in aqueous solution was studied by ¹³C NMR spectroscopy.     

Total Synthesis of Carthamin,a Traditional Natural Red Pigment

The first total synthesis of carthamin ( 3 ), a historic natural red pigment, has been achieved. The molecular structure was efficiently constructed by assembling two equivalents of the in situ generated lithiated monomers and triisopropyl orthoformate. This synthesis confirms the structure proposed in 1996.     

Total Synthesis of Carthamin,a Traditional Natural Red Pigment

The first total synthesis of carthamin ( 3 ), a historic natural red pigment, has been achieved. The molecular structure was efficiently constructed by assembling two equivalents of the in situ generated lithiated monomers and triisopropyl orthoformate. This synthesis confirms the structure proposed in 1996.     

Preparation of 1-dialkylamino-1,2,3-trienes,a novel type of cumulenes

Solutions of α-lithiated cumulenic amines are produced upon treatment of l-dialkylamino-4-methoxy-4-methyl-2-pentynes with two equivalents of butyllithium. Subsequent protonation with t-butyl alcohol gives the corresponding cumulenic amines, while treatment with trimethylchlorosilane gives the α-trimethylsilylated derivatives.     

α,β-Unsaturated diimines as substrates in catalytic C-H activation reactions and as ligands in iron carbonyl complexes

The reaction of 3-[4-(3-oxo-propenyl)-phenyl]-propenal with two equivalents cyclohexylamine as well as the treatment of cyclohexane-1,4-diamine or bis-(4-aminocyclohexyl)-methane with two equivalents of cinnamaldehyde leads to the formation of the corresponding diimines. Mono- or dinuclear iron carbonyl complexes are produced if the diimines are reacted with iron carbonyls. Two of these complexes have been characterized by X-ray crystallography showing that one or two of the α,β-unsaturated imine side chains are coordinated by an iron tricarbonyl moiety in a η⁴-fashion. The packing is realized by intermolecular C-H?O contacts. The same diimines are used as the substrates in ruthenium catalyzed C-H activation reactions together with carbon monoxide and ethylene to produce bis-dihydropyrrolone derivatives in almost quantitative yields.     

Reactions of dichloromaleimides with alcohols,phenols, and thiols

Thiols react with dichloromaleimides in the presence of base to give 2,3-bis[alkyl(aryl)-mercapto]maleimides. Alcohols and phenols in equivalent amounts give 2-alkyl(aryl)oxy-3-chloromaleimides. With two equivalents, phenols give 2,3-bis(aryloxy)maleimides, but alcohols give 2-chloro-3,3-dialkoxysuccinimides in protic solvents and dimeric compounds in aprotic solvents.     

One-pot palladium-catalyzed highly chemo-, regio-, and stereoselective synthesis of trans-stilbene derivatives. A concise and convenient synthesis of resveratrol

A convenient, efficient and highly chemo-, regio-, and stereoselective one-flask synthetic method is reported for the construction of unsymmetrical (or symmetrical) trans-stilbene derivatives based on two sequential Heck-type reactions using tetraalkylammonium salt-based catalyst systems and vinyltrimethylsilane as double bond equivalents. Resveratrol has thus been concisely synthesized.     

Nitrogen–Carbon Bond Formation by Reactions of a Titanium–Potassium Dinitrogen Complex with Carbon Dioxide,tert‐Butyl Isocyanate,and Phenylallene

Nitrogen–carbon bond‐forming reactions at coordinated dinitrogen in a bifunctional titanium–potassium system are reported. A titanium atrane complex with a tris(aryloxide)methyl ligand ( 1 ) was treated with two equivalents of potassium naphthalenide under N₂ atmosphere to generate a bifunctional complex ( 2 ) in which N₂ binds end‐on to two titanium centers and side‐on to three potassium cations. Dinitrogen complex 2 reacted with carbon dioxide, tert ‐butyl isocyanate, and phenylallene, forming nitrogen–carbon bonds and affording diverse N‐functionalized products. The reaction of 2 with CO₂ followed by addition of Me₃SiCl resulted in the formation of the starting complex 1 with concomitant release of silylated carboxyl hydrazines while the reaction with two equivalents of tert ‐butyl isocyanate proceeded by insertion into the Ti−N bonds. Treatment of 2 with phenylallene afforded vinyl‐substituted hydrazido complexes.     

Push-pull alkenes by reacting N,N′-dimethyl cyclic ketene N,N′-acetals with isocyanates: synthesis, structures, and reactivities

N,N′-Dimethyl cyclic ketene N,N′-acetals react with two or three equivalents of isocyanates to generate tetrasubstituted push-pull alkene derivatives in one-pot sequential reactions. X-ray crystallography showed significant elongations and out of plane distorsions of the polarized carbon-carbon double bonds.     

First synthesis of S,S-dialkyl difluorophosphonodithioates and difluorophosphonotrithioates

Several dialkyl difluoromethylphosphonodithioates and difluoromethylphosphonotrithioates have been prepared from difluoromethylphosphonyl dichloride and two equivalents of alkanethiols under basic conditions. Treatment of these species with LDA at low temperatures mainly resulted in decomposition, and to the low-yield isolation of difluorophosphinates or phosphine oxides, thus reflecting the lability of the P-S bond. The desired difluorophosphonodithioates and difluorophosphonotrithioates can be efficiently prepared by reversing the sequence of reactions.     

Silica Sulfuric Acid‐Catalyzed Five‐component Efficient Synthesis of Five‐Substituted Tetrahydropyridines

A highly atom‐economic one‐pot synthesis of five‐substituted tetrahydropyridines via a five‐component condensation of two equivalents of aromatic aldehyde, two equivalents of aromatic aniline, and one equivalent of β‐keto ester catalyzed by silica sulfuric acid is reported. In this reaction, up to five new bonds and one new ring were formed in one pot with water as the only one by‐product.     

Cyclic imides. XI. Bisimide charge-transfer polymers

Condensation of two equivalents of an aromatic cyclic anhydride with an aromatic diamine, or of two equivalents of an aromatic amine with an aromatic bisanhydride, results in the formation of an aromatic bisimide. Thirty-one such bisimides were prepared. The bisimides in which the two imide groups arc connected by a fully coplanar system show extremely low solubilities and high melting and decomposition temperatures. Many are also strongly colored. It is suggested that these properties may result from intermolecular charge-transfer effects in the solid slate, giving charge-transfer polymers.