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

Two general methods of synthesis have been developed for the preparation of long-chain beta-diketones. The first relies on malonate-type alkylation of acid chlorides derived from fatty acids, while the second, more direct method, involves coupling and subsequent hydrolysis of long-chain acetylenes with acid chlorides of fatty acids.

General Method of Synthesis for Natural Long-Chain β/-Diketones

A high-yielding method for the N-demethylation of oxycodone- and oxymorphone-N-oxides by the reaction of these compounds with cyclodehydration reagents has been performed. This method has been utilized to improve the synthesis of various morphine analogs, such as naltrexone, nalbuphone and naloxone.

Processes and intermediates in the preparation of morphine analogs via n-demethylation of n-oxides using cyclodehydration reagents

Idesolide was synthesized in five steps from benzoic acid by base-catalyzed dimerization of hydroxy keto ester, obtained from diol, the product of the whole-cell fermentation of benzoic acid with R. eutrophus B9.

Chemoenzymatic synthesis of idesolide from benzoic acid

2-Methylpiperidine and 2-cyclohexylpiperidine were converted to their respective β-keto amides by treatment with diketene. Several strains of yeast were used to reduce the racemic β-keto amides. The unreacted enantiomers were separated from the β-hydroxy amides, the amides cleaved, and the extent of resolution was determined for the cyclic amines. Detailed experimental and spectral data are provided for all compounds.

Preliminary investigation of the yeast-mediated reduction of β-keto amides derived from cyclic amines as potential resolution methodology

This chapter is a combined update of Chapters 8.1 (Hudlicky, T.; Reed, J. W. Rearrangements of Vinylcyclopropanes and Related Systems. In Comprehensive Organic Synthesis ; Trost, B. M., Fleming, I., Eds.; Pergamon: Oxford, 1991 , Chapter 8.1; pp 899–970) and 8.2 (Piers, E. Rearrangements of Divinylcyclopropanes. In Comprehensive Organic Synthesis ; Trost, B. M., Fleming, I., Eds.; Pergamon: Oxford, 1991 , Chapter 8.2; pp 971–998) in the first edition of Comprehensive Organic Synthesis , published in 1991. The introductory parts of each of the previous chapters were incorporated with minimal editing. Relevant new material published after 1990 has been added for both topics along with references to new reviews. The authors published the last major review on the chemistry of vinylcyclopropanes in 2010 to observe the fiftieth anniversary of Neureiter's discovery of the vinycyclopropane–cyclopentene rearrangement (Hudlicky, T.; Reed, J. W. Angew. Chem. Int. Ed. 2010 , 49 , 4864–4876).

Tomas Hudlicky

Papers

General Method of Synthesis for Natural Long-Chain β/-Diketones

Processes and intermediates in the preparation of morphine analogs via n-demethylation of n-oxides using cyclodehydration reagents

Chemoenzymatic synthesis of idesolide from benzoic acid

Preliminary investigation of the yeast-mediated reduction of β-keto amides derived from cyclic amines as potential resolution methodology

5.22 Rearrangements of Vinylcyclopropanes, Divinylcyclopropanes, and Related Systems