Palladium-Promoted Synthesis of Ionophore Antibiotics. Strategy and Assembly of the Homochiral Tetrahydrofuran and Tetrahydropyran Portions of Tetronomycin

Lactones with methylcyclohexane systems obtained by chemical and microbiological methods and their antimicrobial activity

Eight new lactones (δ-chloro-, δ-bromo- and δ-iodo-γ-lactones), each with a methylcyclohexane ring, were obtained by chemical means from (4-methylcyclohex-2-en-1-yl) acetic acid or (6-methylcyclohex-2-en-1-yl) acetic acid. Whole cells of ten fungal strains (Fusarium species, Syncephalastrum racemosum and Botrytis cinerea) were tested on their ability to convert these lactones into other products. Some of the tested fungal strains transformed chloro-, bromo- and iodolactone with a methyl group at C-5 into 2-hydroxy-5-methyl-9-oxabicyclo[4.3.0]nonan-8-one during hydrolytic dehalogenation. When the same lactones had the methyl group at C-3, no structural modifications of halolactones were observed. In most cases, the optical purity of the product was low or medium, with the highest rate for chlorolactone (45.4%) and iodolactone (45.2% and 47.6%). All of the obtained compounds were tested with reference to their smell. Seven halolactones and the hydroxylactone obtained via biotransformation of halolactones with 5-methylcyclohexane ring were examined for their antimicrobial activity. These compounds were capable of inhibiting growth of some bacteria, yeasts and fungi.

Palladium-catalyzed oxidative carbonylation reactions

Palladium-catalyzed coupling reactions have become a powerful tool for advanced organic synthesis. This type of reaction is of significant value for the preparation of pharmaceuticals, agrochemicals, as well as advanced materials. Both, academic as well as industrial laboratories continuously investigate new applications of the different methodologies. Clearly, this area constitutes one of the major topics in homogeneous catalysis and organic synthesis. Among the different palladium-catalyzed coupling reactions, several carbonylations have been developed and widely used in organic syntheses and are even applied in the pharmaceutical industry on ton-scale. Furthermore, methodologies such as the carbonylative Suzuki and Sonogashira reactions allow for the preparation of interesting building blocks, which can be easily refined further on. Although carbonylative coupling reactions of aryl halides have been well established, palladium-catalyzed oxidative carbonylation reactions are also interesting. Compared with the reactions of aryl halides, oxidative carbonylation reactions offer an interesting pathway. The oxidative addition step could be potentially avoided in oxidative reactions, but only few reviews exist in this area. In this Minireview, we summarize the recent development in the oxidative carbonylation reactions.

Stereoselective Synthesis of Saturated Heterocycles via Pd-Catalyzed Alkene Carboetherification and Carboamination Reactions

The development of Pd-catalyzed carboetherification and carboamination reactions between aryl/alkenyl halides and alkenes bearing pendant heteroatoms is described. These transformations effect the stereoselective construction of useful heterocycles such as tetrahydrofurans, pyrrolidines, imidazolidin-2-ones, isoxazolidines, and piperazines. The scope, limitations, and applications of these reactions are presented, and current stereochemical models are described. The mechanism of product formation, which involves an unusual intramolecular syn-insertion of an alkene into a Pd-Heteroatom bond is also discussed in detail.

A Highly Efficient Synthesis of the FGH Ring of Micrandilactone A. Application of Thioureas as Ligands in the Co-catalyzed Pauson−Khand Reaction and Pd-Catalyzed Carbonylative Annulation

The functionalized FGH ring system of micrandilactone A was successfully constructed in high selectivity and good yields. The key reactions in our strategy are the Co-thiourea-catalyzed stereoselective, intramolecular Pauson-Khand reaction and Pd-thiourea-catalyzed stereoselective, intramolecular annulation. [structure: see text]

An Approach toward the Triquinane-Type Skeleton via Reagent-Controlled Skeletal Rearrangements. A Facile Method for Protection-Deprotection of Organomercurials, Tuning the Selectivity of Wagner-Meerwein Migrations, and a New Route to Annulated Lactones

Nonlinear triquinane-type building blocks have been synthesized using three strategic steps, namely, (1) Hg(2+)-mediated opening of a cyclopropane ring involving a skeletal rearrangement (3 --> 8), (2) an intramolecular organometallic addition across a C=O bond triggered by activation of the C-HgX group by means of Me(3)CuLi(2) (14 --> 26), and (3) selective, reagent-controlled skeletal rearrangements (43 --> 47 with Tl(3+) or Hg(2+); 43 --> 51 + 52 with Pd(2+); 44 --> 47 with Pd(2+)). A new method for protection/deprotection of organomercurials has been developed, which allows selective reduction of a carbonyl group with NaBH(4) and other hydrides (8 --> 14 --> 16 --> 20) and Tebbe methylenation (14 --> 31 --> 32). Oxidative demercuration (8 --> 11 + 28) and Pd(2+)-catalyzed carbonylation of organomercurials (20 --> 53) allowed syntheses of gamma- and delta-lactones.

Sequenced Reactions with Samarium(II) Iodide. Sequential Nucleophilic Acyl Substitution/Ketyl Olefin Coupling Reactions for the Preparation of Oxygen Heterocycles

Samarium(II) iodide has been employed to promote a sequential intramolecular nucleophilic acyl substitution/intramolecular ketyl olefin coupling cyclization sequence to provide bicyclic, tricyclic, and spiro-fused oxygen heterocycles in excellent yield and with high diastereoselectivity.