More arrows in the quiver: new pathways and old problems with heavy alkaline earth metal diphenylmethanides

Progress in the field of sigma-bonded alkaline earth organometallics has been handicapped by numerous complications, such as high reactivity, low solubility, and the limited availability of suitable starting materials. Here we present two synthetic methods, hydrocarbon elimination and desilylation, as alternative routes into this chemistry. A novel barium diphenylmethanide was prepared using these routes delineating that both methods provide a powerful, versatile synthetic access route to an extended library of organometallic alkaline earth derivatives.     

Convergent synthesis of the FGHI ring system of yessotoxin: stereoselective construction of the G ring

A convergent synthetic route to the FGHI ring system of yessotoxin, a marine ladder polyether, has been developed. The synthesis features convergent coupling of the diol and the aldehyde to form α-cyano ethers via acetal formation followed by ring closing metathesis and reductive etherification to construct the oxocane ring G and tetrahydropyran ring H, respectively. The β-methyl group on the G ring was stereoselectively introduced by alkylation of the corresponding ketone.     

Alkyne and ketone induced novel cleavage of a CC bond and a CSi bond in zirconacyclobutene-silacyclobutene fused ring compounds

Novel cleavage patterns of CC bonds and CSi bonds were achieved via alkyne- or ketone-induced reactions of zirconacyclobutene-silacyclobutene fused ring compounds; thermodynamically favored six-membered zirconacyclohexadiene derivatives were formed in excellent yields from the four-membered zirconacyclobutenes via this unprecedented alkyne-induced CC bond and CSi bond cleavage process.     

Rapid access to epothilone analogs via semisynthetic degradation and reconstruction of epothilone D

A facile and efficient route to epothilone analogs has been developed from the natural product epothilone D (1). Degradation of 1 via an oxidative cleavage sequence provides acid intermediate 4 rapidly in six steps. From 4, a variety of epothilone analogs have been prepared utilizing ring-closing metathesis to reconstruct the trisubstituted-12,13-double bond. Using this approach, we report a number of epothilone analogs with varying C-15 aromatic side chains and C-14 allylic substitutions and their biological activities.     

A concise synthesis of highly functionalized α,β-unsaturated γ-butyrolactones through ring contraction of 2H-pyran-2-ones

2-Oxo-5-(1-arylvinyl)-4-piperidin-1-yl-2,5-dihydrofuran-3-carbonitriles 3 have been synthesized through ring contraction of suitably functionalized 2H -pyran-2-ones 1 by a carbanion generated in situ from nitromethane 2 in good yield. In some cases their counterpart tautomers 2-oxo-5-(1-arylethylidene)-4-piperidin-1-yl-2,5-dihydrofuran-3-carbonitriles 4 have also been isolated and characterized as minor products.     

Copper-catalyzed oxidative cleavage of carbon-carbon double bond of enol ethers with molecular oxygen

A novel CC bond cleavage reaction of aromatic enol ethers (1) to give ketones (2) using molecular oxygen as oxidant is described. Among the examined catalysts (Cu(II), Pd(II), Ru(II), and H⁺), CuCl₂ exhibited the highest activity. The reaction proceeded smoothly with several kinds of substrates.     

Microwave-assisted palladium-catalyzed allylation of aryl halides with homoallyl alcohols via retro-allylation

The palladium-catalyzed allylation of aryl halides with homoallyl alcohols via retro-allylation proceeds at 200-250 °C in a toluene-DMF mixed solvent using microwave heating. Even at such high temperatures, the regio- and stereospecificity of the allyl transfer reaction is still satisfactory. The amount of the palladium catalyst can be reduced to 0.5 or 0.05 mol %.     

四氢呋喃开环均聚以及四氢呋喃和环硫氯丙烷共聚新催化体系

研究发现无水稀土氯化物 ５０％发烟硫酸体系是四氢呋喃（ＴＨＦ）均聚和四氢呋喃与环硫氯丙烷（ＣＭＴ）共聚合的优良新催化体系．考察了ＴＨＦ均聚反应特征，在合适条件下，ＴＨＦ聚合以６５％转化率制得粘均分子量达１０，０００～１５，０００的白色聚四氢呋喃（ＰＴＨＦ）固体．端羟基分析法测得聚合物的分子链两端均为羟基．考察了影响ＴＨＦ ＣＭＴ共聚合反应诸因素，如聚合温度和时间、两单体的比例等，制得数均分子量为１，０００左右的淡黄色粘性固体共聚物．     

Characterisation of leather candidate certified reference materials for their mass fractions of aromatic amines

Three batches of leather samples were coloured with nine azo dyes that can yield eight proven or suspected carcinogenic aromatic amines under reduction conditions. The samples were milled to grains and bottled in jars. A group of five laboratories has established the mass fraction of the amines in a ring test using different analytical methods. The methods included a reduction step in order to cleave the azo dyes into the aromatic amines. Quantification was by standard addition: sub-samples of the leathers were spiked with known amounts of azo dyes of known purity. It was possible to establish the mass fractions of six of the eight aromatic amines in three of the leather samples.     

Synthese und Reaktionsverhalten von 6-sec-Amino-1,3-thiazin-2-thionen

The title compounds3 have been prepared by ring transformation reactions of the isomeric 2-sec-amino-1,3-thiazine-6-thiones1 via ring-opening products2 and by special cyclocondensation reactions with thiocarboxamides8, and with iminium salts10, starting from 2,2-dichlorovinyl ketones6 in all cases. The pathways differ specifically in scope and limitations. On the other hand the intermediates2 react with alkylating agents to 2,6-di-sec-amino-1,3-thiazinium salts4, which are also available via alkylation of3 to 2-methylthio-1,3-thiazinium salts11 and aminolysis. Moreover,11 serve as useful precursors for other 1,3-thiazine derivatives by nucleophilic methylthio displacement (examples12).