Max Audouin

A Major Breakthrough in the Use of Alkoxycarbene Complexes of Chromium and Tungsten for the Synthesis of Elaborate Organic Compounds: Dihydropyridine Induced Reductions and Cascade Insertion Reactions

Abstract Alkoxy (alkyl)carbene complexes of tungsten and chromium react with dihydropyridine and N-methyldihydropyridine to give respectively pyridinium ylid complexes and N-methylpyridinium tungstates and chromates. These two types of complexes can be used, for the former, as cyclopropanation reagents, for the latter, as unprecedented initiators of cascade multiinsertions of olefins, alkynes and CO. These insertions lead to elaborate polycyclic compounds.

Interaction of dihydropyridines with alkoxycarbene complexes of tungsten: formation and use as cyclopropanation reagents of pyridinium ylide complexes

Abstract Alkoxycarbene complexes of tungsten, e.g. (CO) 5 WC(CH 3 )OEt ( 13 ) react with 1,2- and 1,4-dihydropyridines, to give, upon transfer of a hydride to the carbene carbon, elimination of ethanol, and readdition of pyridine to an unstable alkylidene complex (CO) 5 WC(H)CH 3 ( 22 ), pyridinium ylide complexes of the type (CO) 5 W − –C(H)(CH3)Py + ( 17 ). A second pyridinium ylide complex (CO) 5 W–C(H)(CH 3 )C 5 H 7 N ( 16 ), and a third dihydropyridinium complex (CO) 5 W–C(H)(CH 3 )C 8 H 11 N ( 15 ), resulting from the interaction of respectively 2,5-dihydropyridine and 5-isopropylidene-2,5-dihydropyridine with (CO) 5 WC(H)(CH 3 ) were also isolated and fully characterized by X-ray crystallography. The origin of the two latter complexes could be established. The new N -ylide complexes react with olefins to give cyclopropanes. Especially interesting, as far as the yields are concerned, is the interaction of highly nucleophilic olefins such as enamines with (CO) 5 W − –C(H)PhPy + ( 25 ) which leads to isomeric cyclopropylamines. The mechanism of their formation will be discussed.

Stereochemistry, part. 62—Acetolysis of triterpenoid p-toluenesulfonates, part 2☆☆☆★★★

Abstract Synthesis of p -toluenesulfonates 8b and 9b and of labelled analogs is described and previous assignements of proton NMR signals for quaternary methyl groups are confirmed. Acetolysis of these p -toluenesulfonates in the presence of NaOAc gave both substitution and elimination products. Substitution could be accounted for by bimolecular processes (SN2 on carbon, S A N on sulfur). Kinetics confirmed the intervention of bimolecular processes for 8b . Elimination products came for a great part from intermediates formed by hydride and/or methyl shifts. All rearranged products could be explained by plain sigmatropic rearrangements or by contact ion pair rearrangements. Attention is drawn to the close resemblance between sigmatropic rearrangements and contact ion pair rearrangements.