Efficient and stereoselective synthesis of beta-trifluoromethyl alpha,beta-unsaturated esters via iron(III) porphyrin-catalyzed olefination of ketones

Reactivity of Nickel Complexes Bearing P(C=X)P Ligands (X = O, N) Toward Diazoalkanes: Evidence for Phosphorus Ylide Intermediates

Nickel carbenes are attracting attention for the development of more sustainable catalysts, among others, for cyclopropanation. Intramolecular trapping of a nickel carbene intermediate with an olefin incorporated in a P(C=C)P Ni pincer complex had previously allowed the isolation of a nickelacyclobutane intermediate and a detailed characterization of its reactivity. Herein, we report the reactivity of related nickel pincer complexes bearing a ketone P(C=O)P or an imine P(C=N)P with diazoalkanes as the carbene precursor. The observed reactivity suggests, in both cases, the reaction of the transient nickel carbene with one of the phosphine arms to form phosphorus ylides that subsequently react with the unsaturated backbone. Density functional theory (DFT) calculations are used to shed light on the mechanisms of these reactions.

Iron(II) Phthalocyanine-Catalyzed Olefination of Aldehydes with Diazoacetonitrile: A Novel Approach to Construct Alkenyl Nitriles

A novel synthetic approach to preparing alkenyl nitriles via the olefination of aldehydes with diazoacetonitrile catalyzed by iron(II) phthalocyanine in the presence of PPh3 has been developed. A broad variety of aldehydes are efficiently transformed into the corresponding products with the high yields of 75%-97%. And it is also suitable for its gram-scale preparation. The suggested mechanism involves the transformation of the phosphazine to ylide by iron(II) phthalocyanine.

Iron-catalyzed transformations of diazo compounds

Although iron-promoted diazo transformations were only discovered during the 1990s, iron can undergo facile changes in its oxidation state and possesses distinct Lewis acid character, and these properties have afforded iron a privileged position as a catalyst in the transformations of diazo compounds. In this review, we have provided an overview of the iron-catalyzed diazo transformation reactions reported in the literature by the end of 2013 with the aim of stimulating further interest in this area of research.

Ph3As-Catalyzed Wittig-Type Olefination of Aldehydes with Diazoacetate in the Presence of Na2S2O4

In the presence of sodium hydrosulfite and a catalytic amount of AsPh3 and Fe(TCP)Cl, aldehydes react with ethyl diazoacetate to give the corresponding alpha,beta-unsaturated esters in high yields with excellent stereoselectivities (E/Z > 50/1).

Asymmetric cyclopropanation of styrenes catalyzed by metal complexes of D2-symmetrical chiral porphyrin: superiority of cobalt over iron

The cobalt(II) complex of D2-symmetric chiral porphyrin [Co(1)] is an effective catalyst for highly diastereoselective and enantioselective cyclopropanation of a broad range of styrene derivatives under mild conditions. Dimerization of diazo compounds, a common side reaction in metal-mediated carbene transfer processes, is minimized in a cobalt porphyrin-based system, obviating the need to employ excess substrates and slow addition of diazo compounds. The high catalytic activity and selectivity of [Co(1)] evidently resulted from the appropriate combination of the cobalt ion and the chiral porphyrin 1 as the use of iron(III) complex of the same ligand [Fe(1)Cl] afforded the desired cyclopropane products in low yields and poor enantioselectivity.

Cobalt-catalyzed efficient aziridination of alkenes

[reaction: see text]. Cobalt porphyrins are capable of catalyzing the aziridination of alkenes with bromamine-T as the nitrene source. Among cobalt complexes of different porphyrins, Co(TDClPP) is an effective catalyst that can aziridinate a wide variety of alkenes. The catalytic system can operate at room temperature in a one-pot fashion with alkenes as limiting reagents, forming the desired N-sulfonylated aziridine derivatives in high to excellent yields with NaBr as the byproduct.

Iron(III) porphyrin catalyzed aziridination of alkenes with bromamine-T as nitrene source

[reaction: see text] Iron(III) porphyrin complexes Fe(Por)Cl are effective catalysts for aziridination of alkenes using bromamine-T as the nitrene source. The catalytic system can operate under mild conditions with alkenes as limiting reagents. The aziridination reaction is general and suitable for a wide variety of alkenes, including aromatic, aliphatic, cyclic, and acyclic olefins, as well as alpha,beta-unsaturated esters. For 1,2-disubstituted olefins, the reactions proceeded with moderate to low stereospecificity.

Oxorhenium Complexes as Aldehyde-Olefination Catalysts

Several oxorhenium compounds in the formal oxidation states V and VII are examined as catalysts for the aldehyde-olefination starting from diazo compounds, phosphines, and aldehydes. Of these, [ReMeO2(eta2-alkyne)] complexes provide the simplest catalysts to study, although [ReOCl3(PPh3)2] still remains the most efficient rhenium catalyst for aldehyde-olefination described to date. Prior to the reaction with the Re catalysts the phosphine and the diazo compound react to form a phosphazine. No catalytic reaction occurs in cases where no phosphazine formation is observed. The first step of the catalytic cycle involves the formation of a carbene intermediate by the reaction of phosphazine and catalyst under extrusion of phosphine oxide and dinitrogen. In a second step the carbene reacts with aldehyde under olefin formation and catalyst regeneration. Excess of alkyne as well as the presence of ketones slows down the catalytic reaction. The olefination of 4-nitrobenzaldehyde with diazomalonate is possible with these Re catalysts. In contrast, this reaction does not take place either in the classical Wittig fashion from Ph3P=C(CO2Et)2 and aldehyde or by use of all other catalysts for aldehyde olefination reactions reported to date. Catalytic ylide formation from diazo compounds seems therefore not to be the only pathway through which catalytic aldehyde-olefination reactions can proceed.

Synthesis and Characterization of Pentaerythritol-Derived Oligoglycol and Their Application to Catalytic Wittig-Type Reactions

Several pentaerythritol-derived oligoglycols 1 with free hydroxyl groups are readily prepared by a convergent approach. Quantitative (13)C NMR proves to be an efficient tool for the characterization of oligoglycols. The corresponding telluride of oligoglycol 17 is synthesized and used as a good catalyst for Wittig-type reactions in preparing both disubstituted and trisubstituted olefins in good to high yields.

Vitamin B12 Derivatives as Natural Asymmetric Catalysts: Enantioselective Cyclopropanation of Alkenes

Vitamin B(12) derivatives were found for the first time to be general and efficient catalysts for asymmetric cyclopropanation of alkenes with ethyl diazoacetate (EDA). Among several common derivatives, aquocobalamin (B(12a)) was shown to be the most effective catalyst for a variety of alkenes, providing cis-dominant cyclopropanes in excellent yields and moderate enantioselectivity. Reactivity studies under different conditions suggest that the active species in the proposed catalytic cycle is the base-on cob(II)alamin (B(12r)) that is generated possibly via in situ reduction of B(12a) by EDA.

Diastereoselective and Enantioselective Cyclopropanation of Alkenes Catalyzed by Cobalt Porphyrins

Cobalt(II) porphyrin complexes were shown to be general and efficient catalysts for selective cyclopropanation of alkenes with ethyl diazoacetate (EDA). The catalytic system can operate with alkenes as limiting reagents, requiring only stoichiometric amounts of EDA. The protocol is performed in one-pot fashion without the need of slow addition of EDA. The diastereoselectivity of the current system can be tuned by using different porphyrin ligands or additives, giving either trans- or cis-dominant cyclopropanes. The asymmetric cyclopropanation was also demonstrated with the use of chiral cobalt porphyrin complexes.