Regio- and enantioselective catalytic monoepoxidation of conjugated dienes: synthesis of chiral allylic cis-epoxides

Reactions of Heteroallenes with Salan-based Ti(IV) Complexes: A Joint Experimental and Computational Study

The reaction of Ti(NMe2)4 with the salan ligand precursor H2N2O2H2 led to the formation of [(L*)Ti(NHMe2)2] (L*=N2O2 4-) that forms [(H2N2O2)TiCl2] upon reaction with two equiv. of Me3SiCl. [(L*)Ti(py)2] was obtained from the reaction of [Ti(NtBu)Cl2(py)3] with the sodium salt H2N2O2Na2. Treatment of [(L*)Ti(NHMe2)2] with two equiv. of tBuNCO led to the insertion of the isocyanate molecules into the Ti-Nsalan bonds with the formation of [{L*(N(tBu)CO)2}Ti]. Conversely, the reaction of [(H2N2O2)Ti(OiPr)2] with two equiv. of tBuNCO led to the insertion of one isocyanate molecule into a Ti-Nsalan bond with the formation of [{(HN2O2)(N(tBu)CO)}Ti(OiPr)]. Computational studies were performed to gain insight into the reactivity of isocyanates with salan-based Ti(IV) complexes.

Synthesis of 1,3-Dienes via Ligand-Enabled Sequential Dehydrogenation of Aliphatic Acids

1,3-Dienes are common scaffolds in biologically active natural products as well as building blocks for chemical synthesis. Developing efficient methods for the synthesis of diverse 1,3-dienes from simple starting materials is therefore highly desirable. Herein, we report a Pd(II)-catalyzed sequential dehydrogenation reaction of free aliphatic acids via β-methylene C-H activation, which enables one-step synthesis of diverse E,E-1,3-dienes. Free aliphatic acids of varying complexities, including the antiasthmatic drug seratrodast, were found to be compatible with the reported protocol. Considering the high lability of 1,3-dienes and lack of protecting strategies, dehydrogenation of aliphatic acids to reveal 1,3-dienes at the late stage of synthesis offers an appealing strategy for the synthesis of complex molecules containing such motifs.

6,6′-((Ethane-1,2-diylbis(azanediyl))bis(methylene))bis(2,4-bis(2-phenylpropan-2-yl)phenolate)zirconium(IV) Dichlorido

The salan zirconium complex of formula [(H2N2O2)ZrCl2] (H2N2O2H2 = HOPh’CH2NH(CH2)2NHCH2Ph’OH, where Ph’ = 2,4-(CMe2Ph)C6H2) was synthesized and fully characterized by NMR and single-crystal X-ray diffraction. The solid-state molecular structure of [(H2N2O2)ZrCl2] shows distorted octahedral geometry around the zirconium center with the salan ligand adopting a β-Λ-cis conformation.

Synthesis and Application of New Salan Titanium Complexes in the Catalytic Reduction of Aldehydes

Complexes of formula [(H2N2O2)TiCl2] and [(H2N2O2)Ti(OiPr)2] (H2N2O2H2 = HOPh’CH2NH(CH2)2NHCH2Ph’OH, where Ph’ = 2,4-(CMe2Ph)C6H2) were synthesized by the reaction of the salan ligand precursor H2N2O2H2 with TiCl4 and Ti(OiPr)4, respectively, in high yields. The dichlorido complex [(H2N2O2)TiCl2] revealed to be an efficient catalyst for the reduction of benzaldehyde in toluene. Full conversion was observed after 24 h at 55 °C in THF. The same catalyst also converted phenylacetaldehyde and hydrocinnamaldehyde into the corresponding alkanes quantitatively.

Methyltrioxorhenium (MTO) catalysis in the epoxidation of alkenes: a synthetic overview

Epoxides are biologically important moiety that is also used as synthetic intermediates. This review aims to present the up-to-date advancements in methyltrioxorhenium (MTO)-catalyzed epoxidation of alkenes using diverse oxidizing agents.

Titanium catalysis for the synthesis of fine chemicals – development and trends

Atlas as a Titan(ium) is holding the earth-abundant chemistry world. Titanium is the second most abundant transition metal, is a key player in important industrial processes (e.g. polyethylene) and shows much promise for diverse applications in the future.

A Heck-Based Strategy To Generate Anacardic Acids and Related Phenolic Lipids for Isoform-Specific Bioactivity Profiling

A synthetic strategy for phenolic lipids such as anacardic acid and ginkgolic acid derivatives using an efficient and selective redox-relay Heck reaction followed by a stereoselective olefination is reported. This approach controls both the alkene position and stereochemistry, allowing the synthesis of natural and unnatural unsaturated lipids as single isomers. By this strategy, the activities of different anacardic acid and ginkgolic acid derivatives have been examined in a matrix metalloproteinase inhibition assay.

A convergent approach to batzelladine alkaloids. Total syntheses of (+)-batzelladine E, (-)-dehydrobatzelladine C, and (+)-batzelladine K

We recently reported a convergent strategy to access the polycyclic guanidinium alkaloid (+)-batzelladine B via an aldol addition-retro-aldol-aza-Michael addition cascade. Here we describe the application of this approach toward the total syntheses of (+)-batzelladine E, (-)-dehydrobatzelladine C, and (+)-batzelladine K. The identification of suitable methods to functionalize a common tropane core by electrophilic alkynylation and nucleophilic 1,2-addition were essential to generalizing this approach. We provide evidence for the intermediacy of an acylallene species in the cascade reaction.

Titanium Salan/Salalen Complexes: The Twofaced Janus of Asymmetric Oxidation Catalysis

Optically pure chiral epoxides and sulfoxides are ubiquitous building blocks in fine organic synthesis, employed in the pharmaceutical, agrochemical, and cosmetic industries. On the road to chiral epoxides and sulfoxides, efficient and stereoselective transition metal-based catalysts are the most promising guides. Among transition metals, we favor titanium for its cheapness and availability, nontoxicity, and well-known ability to catalyze a variety of stereoselective transformations, including oxidations with environmentally benign H2O2. In this personal account, we summarize the state-of-the-art of rational design of chiral titanium(IV) salan and salalen catalysts, and investigations of their catalytic reactivities and stereoselectivities in the epoxidations of olefins and oxidations of thioethers, unraveling the peculiarities and mechanisms of their catalytic action.

Asymmetric Epoxidation Using Hydrogen Peroxide as Oxidant

Asymmetric epoxidation is one of the most important transformations in organic synthesis. Although tremendous progress was achieved in this field in the 1980s and 1990s, it is still desirable from both economical and ecological views to develop environmentally friendly catalytic epoxidation with a broad substrate scope. Hydrogen peroxide is a safe and cheap oxidant, which is easy to handle and generates water as the sole byproduct. Therefore, asymmetric epoxidation of olefins using hydrogen peroxide as oxidant has been a very active research field and has been investigated by many research groups in recent years. In this review, the exciting very recent developments of this rapidly growing area are surveyed and organized according to the catalyst systems.