Synthesis and activity of a new generation of ruthenium-based olefin metathesis catalysts coordinated with 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene ligands.

ion. The oxidative addition mechanism was originally proposed22i because of the lack of a strong rate dependence on polar factors and on the acidity of the medium. Later, however, the electrophilic substitution mechanism also was proposed. Recently, the oxidative addition mechanism was confirmed by investigations into the decomposition and protonolysis of alkylplatinum complexes, which are the reverse of alkane activation. There are two routes which operate in the decomposition of the dimethylplatinum(IV) complex Cs2Pt(CH3)2Cl4. The first route leads to chloride-induced reductive elimination and produces methyl chloride and methane. The second route leads to the formation of ethane. There is strong kinetic evidence that the ethane is produced by the decomposition of an ethylhydridoplatinum(IV) complex formed from the initial dimethylplatinum(IV) complex. In D2O-DCl, the ethane which is formed contains several D atoms and has practically the same multiple exchange parameter and distribution as does an ethane which has undergone platinum(II)-catalyzed H-D exchange with D2O. Moreover, ethyl chloride is formed competitively with H-D exchange in the presence of platinum(IV). From the principle of microscopic reversibility it follows that the same ethylhydridoplatinum(IV) complex is the intermediate in the reaction of ethane with platinum(II). Important results were obtained by Labinger and Bercaw62c in the investigation of the protonolysis mechanism of several alkylplatinum(II) complexes at low temperatures. These reactions are important because they could model the microscopic reverse of C-H activation by platinum(II) complexes. Alkylhydridoplatinum(IV) complexes were observed as intermediates in certain cases, such as when the complex (tmeda)Pt(CH2Ph)Cl or (tmeda)PtMe2 (tmeda ) N,N,N′,N′-tetramethylenediamine) was treated with HCl in CD2Cl2 or CD3OD, respectively. In some cases H-D exchange took place between the methyl groups on platinum and the, CD3OD prior to methane loss. On the basis of the kinetic results, a common mechanism was proposed to operate in all the reactions: (1) protonation of Pt(II) to generate an alkylhydridoplatinum(IV) intermediate, (2) dissociation of solvent or chloride to generate a cationic, fivecoordinate platinum(IV) species, (3) reductive C-H bond formation, producing a platinum(II) alkane σ-complex, and (4) loss of the alkane either through an associative or dissociative substitution pathway. These results implicate the presence of both alkane σ-complexes and alkylhydridoplatinum(IV) complexes as intermediates in the Pt(II)-induced C-H activation reactions. Thus, the first step in the alkane activation reaction is formation of a σ-complex with the alkane, which then undergoes oxidative addition to produce an alkylhydrido complex. Reversible interconversion of these intermediates, together with reversible deprotonation of the alkylhydridoplatinum(IV) complexes, leads to multiple H-D exchange

Activation of c-h bonds by metal complexes

Dioxygen activation at mononuclear nonheme iron active sites: enzymes, models, and intermediates.

Electrochemistry represents one of the most intimate ways of interacting with molecules. This review discusses advances in synthetic organic electrochemistry since 2000. Enabling methods and synthetic applications are analyzed alongside innate advantages as well as future challenges of electroorganic chemistry.

Synthetic Organic Electrochemical Methods Since 2000: On the Verge of a Renaissance

Kinetics of II-VI and III-V Colloidal Semiconductor Nanocrystal Growth: “Focusing” of Size Distributions

Design Constraints in Practical Syntheses of Complex Molecules: Current Status, Case Studies with Carbohydrates and Alkaloids, and Future Perspectives.

Whole-cell biooxidation of bromobenzene with Pseudomonas putida 39D or the recombinant Escherichia coli JM109 (pDTG601) yields (1S,2S)-3-bromocyclohexa-3,5-diene-1,2-diol (9a), which is protected as the acetonide and converted to vinylaziridines 7, 15a, 63, and 64. Our route to (+)-pancratistatin features the coupling of a higher order cyanocuprate (derived by ortho-metalation from N,N-dimethyl-2-[(tert-butyldimethylsilyl)oxy]-3,4-(methylenedioxy)benzamide) with aziridine 7 to generate 28, which contains the carbon framework of the title alkaloid. Functional group manipulations resulted in the preparation of epoxydiol 50, which was transformed in a unique fashion and under mild conditions (H2O/PhCO2Na) to (+)-pancratistatin, thus completing a concise synthesis of (+)-pancratistatin in 14 steps from bromobenzene (2% overall yield). To improve this first generation attempt, a new route was devised utilizing carbomethoxyaziridine 64 and its coupling to the cuprate of 3,4-(methylenedioxy)bromobenzene. The add...

Toluene Dioxygenase-Mediated cis-Dihydroxylation of Aromatics in Enantioselective Synthesis. Asymmetric Total Syntheses of Pancratistatin and 7-Deoxypancratistatin, Promising Antitumor Agents1

Both enantiomers of the pyrrolizidine alkaloid trihydroxyheliotridane 1 have been prepared in an efficient and stereocontrolled fashion in 10 steps. Key steps involve the microbial oxidation of chlorobenzene with Pseudomonas putida to afford chiral cyclohexadienediol4 with high enantiomeric excess and its conversion to lactone 7, from which either enantiomer of azide 18 can be prepared. The azides are converted to the title compounds via a [4 + 11 pyrroline annulation based on an intramolecular azidediene cycloaddition/thermal rearrangement.

Microbial oxidation of chloroaromatics in the enantiodivergent synthesis of pyrrolizidine alkaloids: trihydroxyheliotridanes

Chapter headings. Preface. Naturally occurring cyclobutanes. Diels-alder reactions in the synthesis of higher terpenes. The asymmetric synthesis of unnatural -amino acids as building blocks for complex molecular synthesis. The role of organic synthesis in the generation of molecular diversity. Biographical sketches of the contributors. Index.

Organic Synthesis: Theory and Applications

Le cis-toluenediol est obtenu par biodegradation du toluene par Pseudomonas putida, souche 39D, et est un substrat pour la synthese de prostaglandine

Tomas Hudlicky

Papers

Design Constraints in Practical Syntheses of Complex Molecules: Current Status, Case Studies with Carbohydrates and Alkaloids, and Future Perspectives.

Toluene Dioxygenase-Mediated cis-Dihydroxylation of Aromatics in Enantioselective Synthesis. Asymmetric Total Syntheses of Pancratistatin and 7-Deoxypancratistatin, Promising Antitumor Agents1

Microbial oxidation of chloroaromatics in the enantiodivergent synthesis of pyrrolizidine alkaloids: trihydroxyheliotridanes

Organic Synthesis: Theory and Applications

Enantioselective synthesis through microbial oxidation of arenes. 1. Efficient preparation of terpene and prostanoid synthons