Direct synthesis of amides from nonactivated carboxylic acids using urea as nitrogen source and Mg(NO) or imidazole as catalysts.

A new method for the direct synthesis of primary and secondary amides from carboxylic acids is described using Mg(NO)·6HO or imidazole as a low-cost and readily available catalyst, and urea as a stable, and easy to manipulate nitrogen source. This methodology is particularly useful for the direct synthesis of primary and methyl amides avoiding the use of ammonia and methylamine gas which can be tedious to manipulate. Furthermore, the transformation does not require the employment of coupling or activating agents which are commonly required.

Iron-Catalyzed Borrowing Hydrogen β-(sp)-Methylation of Alcohols.

Herein we report the iron-catalyzed (sp)-methylation of primary alcohols using methanol as a C1 building block. This borrowing hydrogen approach employs a well-defined bench-stable (cyclopentadienone)iron(0) carbonyl complex as precatalyst (5 mol %) and enables a diverse selection of substituted 2-arylethanols to undergo (sp)-methylation in good isolated yields (24 examples, 65% average yield).

One-Pot Conversion of Allylic Alcohols to α-Methyl Ketones via Iron-Catalyzed Isomerization-Methylation.

A one-pot iron-catalyzed conversion of allylic alcohols to α-methyl ketones has been developed. This isomerization-methylation strategy utilized a (cyclopentadienone)iron(0) carbonyl complex as precatalyst and methanol as the C1 source. A diverse range of allylic alcohols undergoes isomerization-methylation to form α-methyl ketones in good isolated yields (up to 84% isolated yield).

Iron-Catalyzed Borrowing Hydrogen C-Alkylation of Oxindoles with Alcohols.

A general and efficient iron-catalyzed C-alkylation of oxindoles has been developed. This borrowing hydrogen approach employing a (cyclopentadienone)iron carbonyl complex (2 mol %) exhibited a broad reaction scope, allowing benzylic and simple primary and secondary aliphatic alcohols to be employed as alkylating agents. A variety of oxindoles underwent selective mono-C3-alkylation in good-to-excellent isolated yields (28 examples, 50-92 % yield, 79 % average yield).

Exploring Tandem Ruthenium-Catalyzed Hydrogen Transfer and SAr Chemistry.

A hydrogen-transfer strategy for the catalytic functionalization of benzylic alcohols via electronic arene activation, accessing a diverse range of bespoke diaryl ethers and aryl amines in excellent isolated yields (38 examples, 70% average yield), is reported. Taking advantage of the hydrogen-transfer approach, the oxidation level of the functionalized products can be selected by judicious choice of simple and inexpensive additives.

Formyloxyacetoxyphenylmethane as an N-Formylating Reagent for Amines, Amino Acids, and Peptides.

Formyloxyacetoxyphenylmethane is a stable, water-tolerant, N-formylating reagent for primary and secondary amines that can be used under solvent-free conditions at room temperature to prepare a range of N-formamides, N-formylanilines, N-formyl-α-amino acids, N-formylpeptides, and an isocyanide.

Acetic acid as a catalyst for the N-acylation of amines using esters as the acyl source.

We report a cheap and simple method for the acetylation of a variety of amines using catalytic acetic acid and either ethyl acetate or butyl acetate as the acyl source. Catalyst loadings as low as 10 mol% afforded acetamide products in excellent yields at temperatures ranging from 80-120 °C. The methodology can also be successfully applied for the synthesis of a broad range of other amides, including the formation of formamides at 20 °C.

DBN hexafluorophosphate salts as convenient sulfonylating and phosphonylating agents.

Air-stable N-sulfonyl and N-phosphonyl DBN hexafluorophosphate salts have been synthesised under mild conditions as sulfonylating and phosphonylating agents. These salts are highly efficient in the sulfonylation and phosphonylation of a range of N- and O-nucleophiles to generate sulfonamides, sulfonate esters, phosphoramidates and phosphonate esters in good yields.

A mild hydration of nitriles catalysed by copper(ii) acetate.

A simple, mild and general procedure for the hydration of nitriles to amides using copper as catalyst and promoted by N,N-diethylhydroxylamine is described. The reaction can be conducted in water at low temperature in short reaction times. This new procedure allows amides to be obtained from a wide range of substrates in excellent yields.

Conversion of nitroalkanes into carboxylic acids via iodide catalysis in water.

We report a new method for the conversion of nitroalkanes into carboxylic acids that achieves this transformation under very mild conditions. Catalytic amounts of iodide in combination with a simple zinc catalyst are needed to give good conversions into the corresponding carboxylic acids.

Lewis acid activation of pyridines for nucleophilic aromatic substitution and conjugate addition.

A clean, mild and sustainable method for the functionalization of pyridines and their analogues is reported. A zinc-based Lewis acid is used to activate pyridine and its analogues towards nucleophilic aromatic substitution, conjugate addition, and cyclization reactions by binding to the nitrogen on the pyridine ring and activating the pyridine ring core towards further functionalization.

Catalytic SNAr of unactivated aryl chlorides.

We present nucleophilic aromatic substitution of unsubstituted aryl chlorides via a mechanism that is catalytic in [CpRu(p-cymene)]PF6 and involves a Ru(η(6)-arylchloride) intermediate. From the spectroscopic evidence we infer that arene exchange is the rate limiting step in this process and develop several new Ru(ii) complexes that lower the activation barrier to arene exchange.

Synthesis of α,β-unsaturated aldehydes based on a one-pot phase-switch dehydrogenative cross-coupling of primary alcohols.

An efficient one-pot ruthenium-catalyzed hydrogen-transfer strategy for a direct access to α,β-unsaturated aldehydes has been developed. The employment of enolates prepared in situ from alcohols avoided handling unstable aldehydes and provided a very appealing route to different cinnamaldehydes substituted in position 2. A silica-grafted amine was used as phase-switch tag leading to a selective one-pot process in favor of cross-dehydrogenative coupling products.

Synthesis of amines with pendant boronic esters by borrowing hydrogen catalysis.

Amine alkylation reactions of alcohols have been performed in the presence of boronic ester groups to provide products which are known to have use as molecular sensors. The boronic ester moiety could be present in either the alcohol or amine starting material and was not compromised in the presence of a ruthenium catalyst.

Iodide as an activating agent for acid chlorides in acylation reactions.

Acid chlorides can be activated using a simple iodide source to undergo nucleophilic attack from a variety of relatively weak nucleophiles. These include Friedel-Crafts acylation of N-methylpyrroles, N-acylation of sulfonamides, and acylation reactions of hindered phenol derivatives. The reaction is believed to proceed through a transient acid iodide intermediate.

Transamidation of primary amides with amines catalyzed by zirconocene dichloride.

Zirconocene dichloride (Cp(2)ZrCl(2)) has been shown to be an effective catalyst for the transamidation of primary amides with amines in cyclohexane at 80 °C in 5-24 hours. For favourable substrates, the reaction can be performed at temperatures as low as 30 °C.

N-acyl DBN tetraphenylborate salts as N-acylating agents.

Air-stable and crystalline N-acyl DBN tetraphenylborate salts have been synthesized from 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) and the corresponding acyl chloride in the presence of sodium tetraphenylborate.

Amidines, isothioureas, and guanidines as nucleophilic catalysts.

Over the last ten years there has been a huge increase in development and applications of organocatalysis in which the catalyst acts as a nucleophile. Amidines and guanidines are often only thought of as strong organic bases however, a number of small molecules containing basic functional groups have been shown to act as efficient nucleophilic catalysts. This tutorial review highlights the use of amidine, guanidine, and related isothiourea catalysts in organic synthesis, as well as the evidence for the nucleophilic nature of these catalysts.

Direct amide formation from unactivated carboxylic acids and amines.

The direct coupling of unactivated carboxylic acids with amines can be performed in toluene 110 °C in the absence of catalyst. The use of simple zirconium catalysts at 5 mol% loading gave amide formation in as little as 4 h.

Ruthenium-catalysed oxidative synthesis of heterocycles from alcohols.

Ruthenium-catalysed hydrogen transfer has been successfully used for the conversion of alcohols into either 2,3-dihydroquinazolines or quinazolines. The choice of reaction conditions allows for the selective formation of either heterocycle and the methodology can also be applied to the sulfonamide analogue.

Ruthenium bidentate phosphine complexes for the coordination and catalytic dehydrogenation of amine- and phosphine-boranes.

Addition of the amine-boranes H(3)B⋅NH(2)tBu, H(3)B⋅NHMe(2) and H(3)B⋅NH(3) to the cationic ruthenium fragment [Ru(xantphos)(PPh(3))(OH(2))H][BAr(F)(4)] (2; xantphos=4,5-bis(diphenylphosphino)-9,9-dimethylxanthene; BAr(F)(4)=[B{3,5-(CF(3))(2)C(6)H(3)}(4)](-)) affords the η(1)-B-H bound amine-borane complexes [Ru(xantphos)(PPh(3))(H(3)B⋅NH(2)tBu)H][BAr(F)(4)] (5), [Ru(xantphos)(PPh(3))(H(3) B⋅NHMe(2))H][BAr(F)(4)] (6) and [Ru(xantphos)(PPh(3))(H(3)B⋅NH(3))H][BAr(F)(4)] (7). The X-ray crystal structures of 5 and 7 have been determined with [BAr(F)(4)] and [BPh(4)] anions, respectively. Treatment of 2 with H(3)B⋅PHPh(2) resulted in quite different behaviour, with cleavage of the B-P interaction taking place to generate the structurally characterised bis-secondary phosphine complex [Ru(xantphos)(PHPh(2))(2)H][BPh(4)] (9).

Metal-catalysed approaches to amide bond formation.

Amongst the many ways of constructing the amide bond, there has been a growing interest in the use of metal-catalysed methods for preparing this important functional group. In this tutorial review, highlights of the recent literature have been presented covering the key areas where metal catalysts have been used in amide bond formation. Acids and esters have been used in coupling reactions with amines, but aldehydes and alcohols have also been used in oxidative couplings.