3,4,5-Trifluorobenzeneboronic acid: a mild and versatile catalyst for the one-pot synthesis of acyl azides from carboxylic acids

Acyloxyboron intermediates generated from carboxylic acids and 3,4,5-trifluorobenzeneboronic acid react with sodium azide to furnish the corresponding acyl azides in moderate to good yields.     

N,N-Dimethylchlorosulfitemethaniminium chloride (SOCl2-DMF) a versatile dehydrating reagent.

N,N-dimethylchlorosulfitemethaniminium chloride formed from thionyl chloride and dimethylformamide was found and efficient reagent for the synthesis of acyl azides from carboxylic acids and nitriles from oximes. It is also highly efficient for the direct synthesis of beta-lactams from carboxylic acids and imines avoiding the use of acid chlorides.     

Direct Acyl Substitution of Carboxylic Acids: A Chemoselective O‐ to N‐Acyl Migration in the Traceless Staudinger Ligation

A chlorophosphite‐modified, Staudinger‐like acylation of azides involving a highly chemoselective, direct nucleophilic acyl substitution of carboxylic acids is described. The reaction provides the corresponding amides with analytical purity in 32–97 % yield after a simple aqueous workup without the need for a pre‐activation step. The use of chlorophosphites as dual carboxylic acid–azide activating agents enables the formation of acyl C? N bonds in the presence of a wide range of nucleophilic and electrophilic functional groups, including amines, alcohols, amides, aldehydes, and ketones. The coupling of carboxylic acids and azides for the formation of alkyl amides, sulfonyl amides, lactams, and dipeptides is described.     

Modified Pyridinium Chlorochromate Oxidation of Aldehydes to Carbamoyl Azides/Acyl Azides or Carboxylic Acids

Aldehydes are transformed into carbamoyl azides/acyl azides by pyridinium chlorochromate in the presence of sodium azide. Comparable oxidations modified with sodium cyanide generate carboxylic acids from simple aliphatic aldehydes whereas conjugated aldehydes are unreactive.     

Dirhodium(II) Carboxylate Catalyzed Formation of 1,2,3‐Trisubstituted Indoles from Styryl Azides

Dirhodium(II)‐carboxylate complexes were discovered to promote the selective migration of acyl groups in trisubstituted styryl azides to form 1,2,3‐trisubstituted indoles. The styryl azides are readily available in three steps from cyclobutanone and 2‐iodoaniline.     

Regioselective synthesis of the 3,4-dihydrofuro[3,2-d]pyrimidin-2(1H)-one skeleton: a new class of compound

We hereby report the first preparation of the 3,4-dihydrofuro[3,2-d]pyrimidin-2(1H)-one skeleton formed by two controlled Curtius rearrangements of the corresponding acyl azides, prepared from 2-(2-methoxy-2-oxoethyl)furan-3-carboxylate via the hydrazide. Rearrangement of the acyl azides followed by trapping by nucleophiles and intramolecular trapping provided the target compounds.     

Rapid and facile synthesis of acyl azides from acyl halides using a polymer-supported azide ion under heterogeneous conditions

In this article a rapid and facile method for synthesis of acyl azide is described. The cross-linked poly(N-methyl-4-vinylpyridinium) azide ion, [P₄-VP]N₃ is prepared and used as an efficient polymeric reagent for synthesis of acyl azides from acyl halides at room temperature under heterogeneous conditions. Various benzoyl halides, with electron-withdrawing groups as well as electron-donating groups, were transformed into the corresponding benzoyl azides in high to excellent yields in short reaction times. The acyl azide products were characterized by FT-IR, and some of them were also characterized by ¹H-and/or ¹³C-NMR spectroscopy, and physical properties were compared to literature values of known compounds. The spent polymeric reagents can be regenerated and reused for several times without losing their activity. Relative to the reported methods, the present method has the advantages of operational simplicity, mild reaction conditions, fast reaction rates, simple reaction work-up and lower hazardous and potentially explosive nature. Also the present method is the first procedure for the synthesis of acyl azides from acyl halides by using a polymer-supported azide ion under heterogeneous conditions.     

Practical and Efficient Synthesis of Orthogonally Protected α‐2,3‐Diaminopropionic Acid (2,3‐Dap), 2,4‐Diaminobutanoic Acid (2,4‐Dab), and their N‐Methylated Derivatives

The synthesis of orthogonally protected Fmoc‐Dap/Dab (Boc/Z/Alloc)‐OH starting from Fmoc‐Asp/Glu has been described. The salient features of our synthetic strategy involved formation of Fmoc‐Asp/Glu‐5‐oxazolidinone acids, conversion of acid function to acyl azides, Curtius rearrangement, and hydrolysis of the oxazolidinone group.     

Radical azidonation of aldehydes

Aliphatic and aromatic aldehydes can be converted to acyl azides by treatment with iodine azide at 0-25 degrees C. If the reaction is performed at reflux Curtius rearrangement occurs and carbamoyl azides are obtained in 70-97% yield from the aldehyde. The reaction was shown to have a radical mechanism.     

The electronic absorption spectra of some acyl azides molecular orbital treatment

The electronic absorption spectra of benzoyl azide and its derivatives: p-methyl, p-methoxy, p-chloro and p-nitrobenzoyl azide were investigated in different solvents. The observed spectra differ basically from the electronic spectra of aryl azides or alkyl azides. Four intense pi-pi* transitions were observed in the accessible UV region of the spectrum of each of the studied compounds. The contribution of charge transfer configurations to the observed transitions is rather weak. Shift of band maximum with solvent polarity is minute. On the other hand, band intensity is highly dependent on the solvent used. The observed transitions are delocalized rather than localized ones as in the case with aryl and alkyl azides. The attachment of the CO group to the azide group in acyl azides has a significant effect on the electronic structure of the molecule. The arrangements as well as energies of the molecular orbitals are different in acyl azides from those in aryl azides. The first electronic transition in phenyl azide is at 276 nm, whereas that of bezoyle azide is at 251 nm. Ab initio molecular orbital calculations using both RHF/6-311G* and B3LYP/6-31+G* levels were carried out on the ground states of the studied compounds. The wave functions of the excited states were calculated using the CIS and the AM1-CI procedures.     

Iodine(V) reagents in organic synthesis. Dess-Martin periodinane mediated efficient one-pot oxidation of aldehydes to acyl azides

A mild, efficient and general method for the one-step preparation of acyl azides from aldehydes using Dess-Martin periodinane and sodium azide is described.     

Konkurrenzexperimente zum nachweis von acylnitrenen

Photolysis of acyl azides, nitrile oxides and 1,4,2-dioxazolinones yield typical acyl nitrene products. Competition experiments show small differences for the competition constants starting with these precursors.     

REDUCTION OF AZIDES TO AMINES OR AMIDES WITH ZINC AND AMMONIUM CHLORIDE AS REDUCING AGENT

ABSTRACT

Alkyl azides and acyl azides were reduced to the corresponding amines and amides with zinc and ammonium chloride as reducing agent under mild conditions in good to excellent yield.     

The mass spectrometry of some aromatic azides

Bromophenyl azides provide the only exceptions to the observation that nitrogen (N₂) is eliminated from the molecular ions. Splitting out of HCN, C₂H₂ and (in the case of acyl or o-nitroaryl azides) CO are important processes.     

One-pot,direct synthesis of acyl azides from carboxylic acids using Ph2PCl/I2/NaN3 reagent system

A mild,efficient and simple method for the preparation of acyl azides from carboxylic acids using chlorodiphenylphosphine in the presence of molecular iodine and sodium azide is described.     

One-pot three-step synthesis of 1,2,3-triazoles by copper-catalyzed cycloaddition of azides with alkynes formed by a Sonogashira cross-coupling and desilylation

A microwave-assisted, one-pot, three-step Sonogashira cross-coupling-desilylation-cycloaddition sequence was developed for the convenient preparation of 1,4-disubstituted 1,2,3-triazoles starting from a range of halides, acyl chlorides, ethynyltrimethylsilane, and azides.     

Simple and facile method for the preparation of vinyl azides

A synthetic utility of [bis(trifluoroacetoxy)iodo]benzene on α,β-unsaturated carboxylic acid is described. This is the first example of preparation of vinyl azide using α,β-unsaturated carboxylic acids directly by using hypervalent iodine reagent. The advantage of this protocol is characterized with non-toxicity of starting material and shorter reaction times to obtain good preparative yields. The method is also useful for the preparation of acyl azides.     

Azide synthesis with stable nitrosyl salts

Aryl and acyl hydrazines were converted to azides in excellent yields by an equimolar amount of nitrosyl tetrafluoroborate or nitrosyl sulfate.     

THE PHOTOCHEMISTRY OF ACETYL-SUBSTITUTED AROYL AZIDES: THE DESIGN OF PHOTOLABELING AGENTS FOR INERT SITES IN HYDROPHOBIC REGIONS

The photochemistry, photophysics and hydrolytic stability of three substituted aroyl azides were investigated. The azides were selected as model compounds for potential photolabeling agents based on the extreme electrophilic reactivity of aroylnitrenes. Each of the azides studied is a derivative of benzoyl azide containing an acyl group to act as an internal triplet sensitizer and an additional functional group useful for linking the azide to a site-selecting probe molecule. The findings show that benzoyl azides containing the three substituents in a 1,3,5-pattern might be useful for labeling of lipophilic molecules.     

Nucleophilic carbene catalyzed synthesis of 1,2 amino alcohols via azidation of epoxy aldehydes

We report herein a nucleophilic carbene catalyzed redox azidation of epoxyaldehydes. The intermediate beta-hydroxy acyl azides undergo thermal Curtius rearrangement followed by trapping with excess azide to form carbamoyl azides or, in a complementary sequence, by the hydroxy group to form oxazolidinones. Both products are formed in modest to good yields and diastereoselectivities. The use of an enantioenriched triazolium catalyst leads to modest asymmetric induction.