Novel Catalytic Hunsdiecker−Heck (CHH) Strategy toward All-EStereocontrolled Ferrocene-Capped Conjugated Push−Pull Polyenes

Ru(0)-catalysed synthesis of borylated polyene building blocks by cross-dimerisation toward cross-coupling

Conjugated and non-conjugated polyenes are important substructures and are often found in biologically active compounds and natural products. Their preparation often needs multiple steps or iterative reactions and as a result, they have poor step economies. In this feature article, we show a new methodology to prepare these substructures by combinations of cross-dimerisation giving borylated polyenes and subsequent cross-coupling reactions. This divergent reaction strategy allows for the opportunity to access many bioactive compounds and natural products as well as some electronic materials.

Decarboxylative Halogenation of Organic Compounds

Decarboxylative halogenation, or halodecarboxylation, represents one of the fundamental key methods for the synthesis of ubiquitous organic halides. The method is based on conversion of carboxylic acids to the corresponding organic halides via selective cleavage of a carbon-carbon bond between the skeleton of the molecule and the carboxylic group and the liberation of carbon dioxide. In this review, we discuss and analyze major approaches for the conversion of alkanoic, alkenoic, acetylenic, and (hetero)aromatic acids to the corresponding alkyl, alkenyl, alkynyl, and (hetero)aryl halides. These methods include the preparation of families of valuable organic iodides, bromides, chlorides, and fluorides. The historic and modern methods for halodecarboxylation reactions are broadly discussed, including analysis of their advantages and drawbacks. We critically address the features, reaction selectivity, substrate scopes, and limitations of the approaches. In the available cases, mechanistic details of the reactions are presented, and the generality and uniqueness of the different mechanistic pathways are highlighted. The challenges, opportunities, and future directions in the field of decarboxylative halogenation are provided.

New strategy for synthesising conjugated hexatrienylferrocenes via cross-dimerisation

A new strategy giving hexatrienylferrocenes.

Polyethylene Glycol Mediated Kinetic Study of Nitro Decarboxylation ofα,β-Unsaturated Acids by Blau’s Fe(III) Phen Complex

Polyethylene glycol (PEG) mediated kinetic study of nitro decarboxylation ofα,β-unsaturated acids (USA) has been taken up by Blau’s [Fe(III) nitrate-Phen] yellow complex in acetonitrile medium. Kinetics of the reactions indicated Michaelis-Menton type of mechanism and rate law. Reaction rates are significantly influenced by the structural variation and concentration of PEG. Catalysis of PEG was explained on the lines of nonionic micelles such as TX-100 because of their structural resemblance and also due to a slight negative charge developed on polyoxyethylene and cationic form(s) of Fe(III) chelates in the intermediate stages.

(2,2-Dichlorovinyl)ferrocene

The title compound, [Fe(C₅H₅)(C₇H₅Cl₂)], represents a versatile building block for the preparation of π-conjugated redox-active compounds or polymetallic organometallic systems due to the presence of the electrochemically active ferrocenyl unit. It is therefore a potential starting material for the preperation of the corresponding alkyne. In the crystal, the alkenyl unit and the cyclo­penta­dienide ring are almost parallel, with an angle between the best planes of only 10.6 (4)°.

Binding of Amino Acids into a Novel Multiresponsive Ferrocene Receptor Having an Ene Backbone

[reaction: see text] Receptor 1 featuring two open arms, multipoint binding sites, and unsaturated linkers on a ferrocene platform shows strong 1:1 binding to unprotected alpha-amino acids (UV-vis, fluorescence, CV, ITC, NMR, and ESI-MS). NMR and ESI-MS studies suggest an encapsulative binding mode involving the alpha,beta-unsaturated carbonyl residue (site for -NH3+, interaction A) and the terminal -OH groups (site for -COO-, interaction B).

Catalytic hunsdiecker reaction of alpha,beta-unsaturated carboxylic acids: how efficient is the catalyst?

UV-vis spectrophotometry is utilized to measure the relative efficiency of lithium acetate, tetrabutylammonium trifluoroacetate, and triethylamine as catalysts for the conversion of 4-methoxycinnamic acid to 4-methoxy-beta-bromostyrene. In acetonitrile-water as solvent, the efficiency order is lithium acetate > triethylamine > tetrabutylammonium trifluoroacetate. For triethylamine as catalyst, solvent-dependent order is acetonitrile-water > dichloromethane > acetonitrile. Using triethylamine as catalyst (5-20 mol %), cinnamic acids, and propiolic acids are converted to corresponding beta-bromostyrenes and 1-halo-1-alkynes in 60-98% isolated yields within 1-5 min.

A nitro-hunsdiecker reaction: from unsaturated carboxylic acids to nitrostyrenes and nitroarenes

[reaction: see text] The nitrodecarboxylation of aromatic alpha,beta-unsaturated carboxylic acids and ring-activated benzoic acids can be achieved using nitric acid (3 equiv) and catalytic AIBN (2 mol %) in MeCN. From the effect of various additives, the nitrodecarboxylation is postulated to involve the generation of an acyloxy radical RCO(2)(*) by a NO(3)(*) radical followed by attack of a NO(2)(*) radical.

Synthesis of Ferrocenyl Alkenes, Dienes, and Enynes via Samarium Diiodide Promoted Tandem Addition and Dehydration of Ferrocenyl Carbonyls with Halides

A practical method for preparation of ferrocenyl alkenes, dienes, and enynes from ferrocenyl carbonyls was explored. A one-pot operation using samarium diiodide to promote the condensation reactions of ferrocenecarboxaldehyde, acetylferrocene, benzoylferrocene, and butanoylferrocene with benzyl bromides, allyl bromide, propargyl bromide, and 1-bromo-3-chlorobutane gave the olefinic products in very high yields. The condensation reactions were also achieved by using catalytic amounts of SmI(2) with magnesium to regenerate the divalent samarium reducing agent.