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The development of catalyst-controlled stereoselective olefin metathesis processes has been a pivotal recent advance in chemistry. The incorporation of appropriate ligands within complexes based on molybdenum, tungsten and ruthenium has led to reactivity and selectivity levels that were previously inaccessible. Here we show that molybdenum monoaryloxide chloride complexes furnish higher-energy (Z) isomers of trifluoromethyl-substituted alkenes through cross-metathesis reactions with the commercially available, inexpensive and typically inert Z-1,1,1,4,4,4-hexafluoro-2-butene. Furthermore, otherwise inefficient and non-stereoselective transformations with Z-1,2-dichloroethene and 1,2-dibromoethene can be effected with substantially improved efficiency and Z selectivity. The use of such molybdenum monoaryloxide chloride complexes enables the synthesis of representative biologically active molecules and trifluoromethyl analogues of medicinally relevant compounds. The origins of the activity and selectivity levels observed, which contradict previously proposed principles, are elucidated with the aid of density functional theory calculations.

The first examples of catalyst-controlled stereoselective macrocyclic ring-closing metathesis reactions that generate Z-enoates as well as (E,Z)- or (Z,E)-dienoates are disclosed. Reactions promoted by 3.0-10 mol % of a Mo-based monoaryloxide pyrrolide complex proceed to completion within 2-6 h at room temperature. The desired macrocycles are formed in 79:21 to >98:2 Z/E selectivity; stereoisomerically pure products can be obtained in 43-75% yield after chromatography. Utility is demonstrated by application to a concise formal synthesis of the natural product (+)-aspicilin.

Olefin metathesis catalysts provide access to molecules that are indispensable to physicians and researchers in the life sciences (1,2).A persisting problem, however, is the dearth of chemical transformations that directly generate acyclic Zallylic alcohols, including products that contain a hindered neighbouring substituent or reactive functional units such as a phenol, an aldehyde, or a carboxylic acid. Here we present an electronically modified ruthenium--disulfide catalyst that is effective in generating such high-value compounds by cross-metathesis. The ruthenium complex is prepared from a commercially available precursor and an easily generated air-stable zinc catechothiolate. Transformations typically proceed with 5.0 mole per cent of the complex and an inexpensive reaction partner in 4-8 hours under ambient conditions; products are obtained in up to 80 per cent yield and 98:2 Z:E diastereoselectivity. The use of this catalyst is demonstrated in the synthesis of the naturally occurring anti-tumour agent neopeltolide and in a single-step stereoselective gram-scale conversion of a renewable feedstock (oleic acid) to an anti-fungal agent. In this conversion, the new catalyst promotes cross-metathesis more efficiently than the commonly used dichlororuthenium complexes, indicating that its utility may extend beyond Z-selective processes., In 2009, it was demonstrated that a molybdenum (Mo) monopyrrolide aryloxide complex can promote ring-opening/cross-metathesis with high Z selectivity (3). This initial discovery and the attendant stereochemical model paved the [...]

The discovery of catalysts that can be used to synthesize complex organic compounds by enantioselective transformations is central to advances in the life sciences (1); for this reason, many chemists aim to discover catalysts that allow for preparation of chiral molecules as predominantly one mirror-image isomer (2). The ideal catalyst should not contain precious elements (3) and should bring reactions to completion in a few hours through operationally simple procedures. Here we introduce a set of small organic molecules that can catalyse reactions of unsaturated organoboron reagents with imines and carbonyls; the products of the reactions are enantiomerically pure amines and alcohols, which might serve as intermediates in the preparation of biologically active molecules. A distinguishing feature of this catalyst class is the presence of a 'key' proton embedded within their structure. Catalysts are derived from the abundant amino acid valine and are prepared in large quantities in four steps with inexpensive reagents. Reactions are scalable, do not demand stringent conditions, and can be performed with as little as 0.25 mole per cent catalyst in less than six hours at room temperature to generate products in more than 85 per cent yield and ≥ 97:3 enantiomeric ratio. The efficiency, selectivity and operational simplicity of the transformations and the range of boron-based reagents are expected to render this advance important for future progress in syntheses of amines and alcohols, which are useful in chemistry, biology and medicine., Many biologically active molecules contain nitrogen-substituted carbon stereogenic centres. Routes for efficient preparation of enantiomerically enriched homoallylic amines are therefore of considerable consequence (4). Anti-cancer agents aza-epothilones A-D (5) (Fig. [...]

The activation energies are measured for phosphine dissociation and ring-closing metathesis for cationized Grubbs first and second-generation catalysts in the gas phase by deconvolution of the energy-resolved collision-induced dissociation cross-sections of electrosprayed ruthenium carbene complexes. The absolute binding energies have agreed well with the latest density functional theory calculations by using a density functional specifically suited for organometallic thermochemistry.

The synthesis of CpMo[([S.sub.2][C.sub.2][Ph.sub.2]).sub.2] by dithiolene transfer, together with reactions leading to a family of di- and trinuclear heterometallic dithiolene complexes derived from it, are described. The results have shown that one of the Cp ligands of nickelocene can be readily displaced by the bis(dithiolene) complex to give heterobimetallic dithiolene-bridged compound, whereas the removal of the second ring to give Ni[[Mo[([S.sub.2][C.sub.2][Ph.sub.2]).sub.2]Cp].sub.2 is a much slower process.

Author(s): Fanke Meng [1]; Xiben Li [1]; Sebastian Torker [1]; Ying Shi [1]; Xiao Shen [1]; Amir H. Hoveyda (corresponding author) [1] Conjugate (or 1,4-) additions of carbanionic species to [...]

Catalytic enantioselective conjugate addition (ECA) reactions with readily accessible and stereochemically defined E‐, Z‐, di‐ and trisubstituted alkenyl aluminum compounds are disclosed. Transformations are promoted by various NHC‐copper catalysts (NHC=N‐heterocyclic carbene), which are derived from enantiomerically pure sulfonate imidazolinium salts. The desired products were obtained in up to 89% yield and >99:1 e.r.; the alkenyl moiety was transferred with complete retention of its stereochemical identity in all instances. The scope and limitations of the approach, key mechanistic attributes, and representative functionalization are presented as well. [ABSTRACT FROM AUTHOR]