No abstract

The use of metal acetates has allowed the synthesis of NHC complexes without isolation of the free carbene. This route is very useful in cases where the metal acetates are readily available and has been used, for example, for the synthesis of bis(N‐heterocyclic carbene) complexes of palladium(II). In the case of platinum, however, the corresponding acetate is not commercially available and is difficult to synthesize. Previously published syntheses require either an external base (e.g. NaOAc or KOtBu) or a transmetalation step. Here we present a new general synthetic pathway for platinum–bis(carbene) complexes using platinum(II) acetylacetonate as a commercially available metal precursor. Aromatic substituents greatly enhance the stability of the metal complexes against acidic media. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Cholesterol is essential for the survival of the nematode Caenorhabditis elegans. Recent studies have demonstrated that cholesterol derivatives regulate two processes in the life cycle of worms: controlling molting and inducing a specialized non‐feeding larval stage. However, the chemical structure of the cholesterol‐derived signalling molecules for these or any other functions has not yet been identified. Herein, we describe the regio‐ and stereospecific synthesis of a number of cholesterol derivatives. The lithium–ammonia reduction of 4‐cholesten‐3‐one was utilized to develop a general method for the introduction of diverse functional groups at C‐4α of 5α‐cholestan‐3β‐ol. Stereoselective functionalization at C‐7 was achieved starting from 7‐ketocholesterol derivatives. 6‐Keto‐5α‐cholestan‐3β‐ol was utilized for specific functionalizations at C‐6 and C‐7. The structure–activity relationships of the different cholesterol derivatives have been investigated by feeding worms of different genetic background with these compounds. Our study is the first step in assigning the relationships of hormonal activity in C. elegans on the substitution at different positions of cholesterol. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

No abstract

The octaphosphorylation of calix [4]resorcinarenes 1 by 2-dialkylamino-1,3,2-diheterophosphorinanes 2 is described, and the effect of different factors on the structures of the resulting perphosphorylated products 3−5 was studied. Conformation analysis of these compounds by correlated 2D NMR spectroscopy and X-ray diffraction analysis was performed, and it was found that compounds 3−5, like the initial resorcinarenes 1, each have the all-cis configuration of the R groups in the methylidene bridges of the calixarene system, but different orientations of benzene rings and phosphorinane fragments with respect to one another and to the macrocycle plane. Perphosphorylated resorcinarenes 3a−c, 4a and 5a with R = alkyl