A survey of acid catalysts for use in two-step, one-flask syntheses of meso-substituted porphyrinic macrocycles

[reaction: see text] Diverse Lewis acids and Bronsted acids were examined in the two-step, one-flask synthesis of meso-tetraphenylporphyrin, N-confused tetraphenylporphyrin, and tetraphenylsapphyrin. The scope of acid catalysis was found to be very broad, with 35 of 45 acids providing TPP in yields ranging from 5% to 58%. NC-TPP was also widely observed in yields of 1-40%, and TPS was infrequently observed in yields of <1%. Additionally, conditions were found for direct preparation of magnesium TPP and copper TPP.     

Efficient synthesis of meso-substituted corroles in a H2O-MeOH mixture

New and efficient conditions for the synthesis of meso-substituted corroles were developed. The first step, involving the reaction of aldehydes with pyrrole, was carried out in a water-methanol mixture in the presence of HCl. A relatively narrow distribution of aldehyde-pyrrole oligocondensates was obtained through careful control of their solubility in the reaction medium. After thorough optimization of various reaction parameters (cosolvent, reagent, and acid concentration), high yields of bilanes were obtained. Additionally, the bilane derived from 4-cyanobenzaldehyde was isolated, and the oxidative macrocyclization reaction was performed under various reaction conditions (different solvents, different concentrations, and various oxidants). As a result, triphenylcorrole was obtained in the highest yield (32%) reported to date. The scope and limitations studied showed that this method was particularly efficient for moderately reactive aldehydes and those bearing electron-donating groups (yields 14-27%). Using these conditions, corroles bearing strongly electron-donating groups were obtained for the first time. In addition, it was found that the reaction of unhindered dipyrromethanes with aldehydes under analogous conditions afforded trans-A2B-corroles in very high yields (45-56%; 8-fold higher than previously reported) without scrambling. The fact that scrambling was not observed in this reaction despite a very high HCl concentration (0.3 M) is unprecedented. Detailed studies on the oxidation of bilane, derived from sterically hindered dipyrromethane, allowed us to unequivocally establish that the yield of macrocyclization is insensitive to the concentration. It was found the 1H NMR spectra of corroles in deuterated TFA gave very sharp signals.     

A novel pyrrole synthesis via reaction of ketones with N-aminoimides

A new, mild synthesis of pyrroles using N-aminoimides and a ketone is described. The reaction has been utilized in the synthesis of dimeric morphinans containing a connecting pyrrole ring. The reaction appears to proceed through a diacylhydrazone intermediate, and it is suggested that the driving force behind the reaction is the facility with which a protonated imide moiety operates as a leaving group.     

Pt@MOF-177: synthesis, room-temperature hydrogen storage and oxidation catalysis

The gas-phase loading of [Zn(4)O(btb)(2)](8) (MOF-177; H(3)btb=1,3,5-benzenetribenzoic acid) with the volatile platinum precursor [Me(3)PtCp'] (Cp'=methylcyclopentadienyl) was confirmed by solid state (13)C magic angle spinning (MAS)-NMR spectroscopy. Subsequent reduction of the inclusion compound [Me(3)PtCp'](4)@MOF-177 by hydrogen at 100 bar and 100 degrees C for 24 h was carried out and gave rise to the formation of platinum nanoparticles in a size regime of 2-5 nm embedded in the unchanged MOF-177 host lattice as confirmed by transmission electron microscopy (TEM) micrographs and powder X-ray diffraction (PXRD). The room-temperature hydrogen adsorption of Pt@MOF-177 has been followed in a gravimetric fashion (magnetic suspension balance) and shows almost 2.5 wt % in the first cycle, but is decreased down to 0.5 wt % in consecutive cycles. The catalytic activity of Pt@MOF-177 towards the solvent- and base-free room temperature oxidation of alcohols in air has been tested and shows Pt@MOF-177 to be an efficient catalyst in the oxidation of alcohols.     

Lability of the β-diethylaminoethyl group under the conditions of the formation of a pyrrole ring via the Knorr synthesis

The corresponding 3-acetyl- and 3-H-pyrroles are formed along with 2,4-dimethyl-3-(-diethylaminoethyl)-5-carbethoxypyrrole in the condensation of 3-(-diethylaminoethyl)pentane-2,4-dione with isonitrosoacetoacetic (I) and isonitrosomalonic (II) esters.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1643–1645, December, 1973.     

A simple and versatile one-pot synthesis of meso-substituted trans-A2B-corroles

We have developed a new methodology that affords regioisomerically pure trans-A2B-corroles. The corrole formation reaction involves the acid-catalyzed condensation of a dipyrromethane and an aldehyde followed by oxidation with DDQ. Optimal conditions for the condensation were identified after examining various reaction parameters (solvent, acid, concentration, time). The conditions identified (CH2Cl2, [DPM] = 33 mM, [aldehyde] = 17 mM, [TFA] = 1.3 mM (for sterically hindered DPMs) or [TFA] = 0.26 mM (for sterically unhindered DPMs), 5 h, room temperature) resulted in the formation of corroles in 3-25% yield without detectable scrambling. The synthesis is compatible with diverse functionalities: ester, nitrile, ether, fluoro, hydroxy, iodo, nitro, thioacetate, methylsulfoxy. In total 21 corroles of type trans-A2B were prepared. Three exemplary corrole syntheses were successfully carried out at 8 mmol scale. Corroles 23, 30, and 41 (160-600 mg) were obtained in essentially the same yield as in small scale experiments.     

A simple, two-step synthesis of 3-iodoindoles

2-Halo-anilines, protected as the corresponding sulfonamides or carbamates, can be converted very efficiently into 3-iodoindoles by sequential Sonogashira coupling with a 1-alkyne and 5-endo-dig iodocyclisation. Azaindoles can also be obtained using this methodology.     

A survey of nonaqueous conditions for the anodic oxidation of N-butyl alcohol

A survey of nonaqueous conditions for the oxidation of n-butyl alcohol is reported. Oxidation may be effected in the neat alcohol or in moderately dilute solution in acetonitrile. High current yields of butyraldehyde are obtained in the neat alcohol, but in dilute solution n-butyl butyrate is the major product. Lithium fluoborate is superior to lithium nitrate or perchlorate as the supporting electrolyte.     

A one-flask synthesis of Weinreb amides from chiral and achiral carboxylic acids using the deoxo-fluor fluorinating reagent

[structure] The reagent [bis(2-methoxyethyl)amino]sulfur trifluoride (Deoxo-Fluor reagent) converts carboxylic acids to the corresponding acid fluorides, which then react with N,N-dimethylhydroxylamine to give the corresponding Weinreb amides in high yields. The reaction proceeds without racemization when optically active acids are used as the starting material. This method is operationally simple and provides the products in high purity.     

A one-pot,two-step synthesis of 3-deazacanthin-4-ones via sequential Pd-catalyzed Suzuki-Miyaura and Cu-catalyzed Buchwald-Hartwig reactions

3-Deazacanthin-4-one and nine analogues, including the 8-aza analogue, were prepared rapidly and in high yields from 8-iodoquinolones and 2-chloro(het)arylboronic acids. The strategy involves construction of the central B ring via concomitant Pd-catalyzed Suzuki-Miyaura CC and Cu-catalyzed Buchwald-Hartwig CN coupling reactions.     

Refined methods for the synthesis of meso-substituted A3- and trans-A2B-corroles

We have refined a one-pot synthesis of A3-corroles via "3 + 4" condensation of an aldehyde with a pyrrole followed by macrocyclization mediated by DDQ. After thorough examination of various reaction parameters (reactivity of an aldehyde, catalyst, solvent, concentration, time etc.) we have elaborated three different sets of conditions for different types of aromatic aldehydes--highly reactive, moderately reactive and sterically hindered. Thanks to the identification of the key factors influencing the yield of bilanes and the yield of their conversion to corroles we were able to improve yields to ca. 17% for highly reactive aldehydes and ca. 13% for moderately reactive aldehydes. Altogether fourteen A3-corroles have been prepared in 7-21% yield. 5,10,15-Trimesitylcorrole has been obtained for the first time. [2 + 1] Condensation between sterically hindered dipyrromethanes and aldehydes has also been refined and yields of trans-A2B-corroles have been improved by ca. 10%.     

Relay catalysis: combined metal catalyzed oxidation and asymmetric iminium catalysis for the synthesis of bi- and tricyclic chromenes

A catalytic asymmetric oxidative iminium-allenamine cascade allows the use of propargyl alcohols as stable substrates and yields valuable chiral bicyclic 4H-chromenes. A subsequent Michael addition-condensation domino reaction provides complex tricyclic 4H-chromenes in a highly enantioselective fashion.     

A novel cyclization/oxidation strategy for a two-step synthesis of (Z)-aurone

An efficient and facile two-step strategy for the synthesis of (Z)-aurone from arylacetylenes and salicyladehydes, via silver(I) nitrate mediated cyclization/oxidation in the presence of potassium carbonate has been developed. The key feature of our method was delicate cascade reaction, to provide the corresponding (Z)-aurone in high yield and good regio- and stereo selectivity.     

Sulfamic acid as efficient and reusable catalytic system for the synthesis of pyrrole,furan, and thiophene derivatives

Sulfamic acid has been utilized for the first time as an efficient and reusable catalytic system for the synthesis of heteroaromatics such as pyrrole, furan, and thiophene derivatives from 1,4‐diketones. This new procedure offers significant improvements in the reaction rates and yields in a shorter reaction time and a lower reaction temperature contrasted with the reported results. The recovered catalyst can be reused for subsequent runs with only a gradual decrease in activity. The most important feature is that the reaction process is homogeneous whereas the separation process is heterogeneous, which is often seen in other catalysts, and so it is a good character for technical application. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:144–148, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20389     

Conversion of cellulose to glucose and levulinic acid via solid-supported acid catalysis

Cellulose is hydrolyzed to glucose, which is further converted to levulinic acid in the presence of surface-supported Brønsted and Lewis acid catalysts. Nafion catalysts, in particular, have the potential to be recycled or applied to a continuous flow reactor for the synthesis of these biofuel precursors.     

A simple, rapid and efficient protocol for the synthesis of methylthiomethyl esters under Swern oxidation conditions

A rapid, mild and high yielding method for the synthesis of methylthiomethyl esters is reported from the corresponding aliphatic, aromatic and unsaturated carboxylic acids under Swern oxidation conditions using dimethylsulfoxide, oxalyl chloride and triethylamine at low temperature.     

Simple, general, and efficient synthesis of meso-substituted borondipyrromethenes from a single platform

An unprecedented synthesis of 8-substituted-borondipyrromethenes is described starting from 8-thiomethylbodipy 1. Aryl, heteroaryl, alkenyl, and organometallic boronic acids smoothly reacted with 1 in the presence of a catalytic amount of Pd(0) and a stoichiometric amount of Cu(I)-2-thienylcarboxylate under neutral conditions to give the corresponding Bodipy analogues in good to quantitative yields (20 examples). A remarkable reactivity was observed in some cases, e.g., ferrocenylboronic acid gave the product in 98% isolated yield after only 10 min at 55 degrees C.     

A practical, two-step synthesis of 1-alkyl-4-aminopyrazoles

A novel synthesis of N1 alkyl-substituted pyrazoles with a free amino group at the C4 position is described. Commercially available 4-nitropyrazole was found to readily undergo Mitsunobu reactions with primary and secondary alcohols. Subsequent reduction of the nitro group via hydrogenation affords 1-alkyl-4-aminopyrazoles, which are valuable intermediates in the synthesis of pharmaceutically active compounds.