Determination of methylmercury in organic matrices with gas chromatography/ atomic absorption spectrometry

Determinations of methylmercury in biological tissues by gas chromatography with electron-capture detection are often disturbed by electron-capturing compounds simultaneously eluting with the organo-mercury compound.Identification and quantification of methylmercury is improved by interfacing the gas chromatograph to the gas cell of a flameless atomic absorption spectrometer. The construction of the transfer line used is described.     

Cobalt-catalyzed intermolecular [2 + 2 + 2] cycloaddition for the synthesis of 1,3-cyclohexadienes

A cobalt(I)-catalyzed [2 + 2 + 2] cycloaddition reaction between an internal acceptor-substituted alkyne and a terminal alkene leads to the formation of regiochemically enriched polysubstituted 1,3-cyclohexadiene derivatives in acceptable yields when methyl butynoate is used, whereas regiochemically pure products are formed in good yields form phenyl propyonate. The concurrent cyclotrimerization reaction of the alkyne to the corresponding benzene derivative is dependent on the sterical bulk of the alkyne and is considerably reduced with the sterically more hindered alkyne.     

Improved Synthesis of Cyclic Tertiary Allylic Alcohols by Asymmetric 1,2‐Addition of AlMe3 to Enones

The development of an improved protocol for the enantioselective Rh^I/binap‐catalysed 1,2‐addition of AlMe₃ to cyclic enones is reported. ³¹P NMR analysis of the reaction revealed that the catalyst in its resting state is a chloride‐bridged dimer. This insight led to the use of AgBF₄ as an additive for in situ activation of the dimeric precatalyst. Thus, the catalyst loading can now be reduced to only 1 mol % with respect to rhodium. Various 5–7‐membered cyclic enones can be transformed into tertiary allylic alcohols with excellent levels of enantioselectivity and high yields. The obtained products are versatile synthetic building blocks, shown by a highly enantioselective formal total synthesis of the pheromone (?)‐frontalin as well as formation of a bicyclic lactone that has the core structure of the natural flavour component “wine lactone”.     

Synthesis of new thiophenolato hydrido iron(II) complexes and their substitution reactions with alkynes

The novel thiophenolato hydrido iron(II) complexes [cis-Fe(H)(SAr)(PMe₃)₄] (4–6) (Ar = p-BrC₆H₄ (4), p-MeOC₆H₄ (5) and o-MeC₆H₄ (6)) were prepared through the reaction of Fe(PMe₃)₄ with thiophenols ArSH (1–3). Reaction of 6 with trimethylsilylacetylene and phenylacetylene afforded bisalkynyl iron(II) complexes [Fe(PMe₃)₄(CCSiMe₃)₂] (7) and [Fe(PMe₃)₄(CCPh)₂] (9) through elimination of dihydrogen and the formation of thiophenol. The reaction of 5 with 2-methyl-3-butyn-2-ol gave [Fe(PMe₃)₄(CCCMe₂OH)₂] (10). The crystal structures of complexes 4, 7 and 10 were determined by X-ray diffraction. A mechanism for the formation of 7 is proposed.