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PubMed2003

Predicted group 4 tetra-azides M(N3)(4) (M = Ti-Hf, Th): the first examples of linear M-NNN coordination.

Quantum chemical calculations suggest that group 4 tetra-azides M(N(3))(4), where M = Ti, Zr, Hf, and Th, are stable species. They present a unique structural feature; namely, the M-N-N-N fragments are linear. These species are energetically more stable than the corresponding isomers with general formula eta(5)-N(5) -M-eta(7)-N(7), and the Th species, Th(N(3))(4), is the most stable of all. Possible mixed nitride azides NMN(3) were also investigated.

Journal Article↗
PubMed2006

Coexistence of spin canting and metamagnetism in a one-dimensional Mn(III) complex bridged by a single end-to-end azide.

Two manganese(III) azide complexes capped with tetradentate Schiff bases were characterized structurally and magnetically. The replacement of halogens on the Schiff bases leads to a drastic structural alteration from a dimer (1) bridged by phenoxide to a one-dimensional chain (2) linked by azide in a single end-to-end mode. Notably, magnetic studies of 2 show the concomitant existence of spin canting and metamagnetism.

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PubMed2003

From azides to nitro compounds in a few seconds using HOF.CH3CN.

HOF.CH3CN, a very efficient oxygen-transfer agent, was reacted with various azides to form the corresponding nitro compounds in excellent yields and in very short reaction times. The respective nitroso derivatives were found to be intermediates in this reaction. When the azides were reacted with MCPBA or DMDO, no reaction took place, and the starting materials were fully recovered.

Journal Article↗
PubMed2005

Copper-catalyzed hydrative amide synthesis with terminal alkyne, sulfonyl azide, and water.

It is shown for the first time that N-sulfonyl amides can be efficiently prepared by an unconventional approach of the hydrative reaction between terminal alkynes, sulfonyl azides, and water in the presence of copper catalyst and amine base under very mild conditions. The present route is quite general, and a wide range of alkynes and sulfonyl azides are readily coupled catalytically with water to furnish amides in high yields. A variety of labile functional groups are tolerated under the conditions, and the reaction is regioselective in that only terminal alkynes react while double or internal triple bonds are intact. The reaction can be readily scaled up and is also adaptable to a solid-phase procedure with high efficiency.

Journal Article↗
PubMed2001

Mechanism of the addition reaction of alkyl azides to [60]fullerene and the subsequent N2 extrusion to form monoimino-[60]fullerenes.

The 1,3-dipolar cycloaddition of methyl azide to C60 and the subsequent nitrogen elimination from the formed triazoline intermediate to yield the aziridine adduct have been studied using semiempirical and density functional methods. The results obtained show that the addition of methyl azide to C60 takes place in the ring junction between two six-membered rings leading to a closed [6,6]-trizoline intermediate with an energy barrier of about 20 kcal mol-1 and an exothermicity of ca. 2 kcal mol-1 at the B3LYP/6-31G**//AM1 level of theory. The subsequent thermal loss of N2 takes place through a stepwise mechanism in which the cleavage of the N-N single bond precedes the breaking of the N-C bond, with a total activation energy of approximately 45 kcal mol-1. The N2 loss occurs simultaneously with the formation of the new N-C bond. During the process, the steric effects of the leaving N2 molecule prevent the addition of the nitrene substituent to the [6,6]-ring junction attacked initially and force the addition to an adjacent [5,6]-ring junction.

Journal Article↗
PubMed2005

1,2-migration of 2'-oxoalkyl group and concomitant synthesis of 2-C-branched O-, S-glycosides and glycosyl azides via 1,2-cyclopropanated sugars.

Treatment of 2'-oxoalkyl 2-O-Ms(Ts)-alpha-C-mannosides (4, 5, and 6) with base resulted in 1,2-cyclopropanation via an intramolecular SN2 reaction due to their 1,2-trans-diaxial configurations. The 1,2-cyclopropanated sugars (10 and 13) were reacted with various alcohols, thiols, and sodium azide to produce 2-C-branched O- and S-glycosides and glycosyl azides (11, 14-28) in good to excellent yields. In contrast, 1,2-cis 2'-oxoalkyl 2-O-Ms(Ts)-alpha-C-glucoside 9 formed an acyclic conjugated aldehyde (31) under basic conditions, which occurred by 1'-enolation followed by beta-elimination. An intramolecular Michael addition from 31 produced 2-O-Ms-beta-C-glucoside 30 as a major product. However, due to the electron-withdrawing effect exerted by 2-O-Ms compound 31 also undergoes a C2 epimerization to form 32. Thereafter, the intramolecular Michael addition led to the formation of both 1,2-trans 2'-oxoalkyl 2-O-Ms-alpha-C-mannoside 4 and its beta-anomer (33). Because beta-elimination/Michael addition and C2 epimerization are reversible reactions, equilibriums among 9, 31, 30, 32, 33, and 4 were established, which included the transformation of 1,2-cis C-glucoside 9 into 1,2-trans C-mannoside 4. The subsequent 1,2-cyclopropanation of 4 was an irreversible reaction yielding 1,2-cyclopropanated 10 and further conversion to 1,2-migration products (11 and 12).

Combinatorial Chemistry Techniques↗
PubMed2006

Revisiting nucleophilic substitution reactions: microwave-assisted synthesis of azides, thiocyanates, and sulfones in an aqueous medium.

A practical, rapid, and efficient microwave (MW) promoted synthesis of various azides, thiocyanates, and sulfones is described in an aqueous medium. This general and expeditious MW-enhanced nucleophilic substitution approach uses easily accessible starting materials such as halides or tosylates in reaction with alkali azides, thiocyanates, or sulfinates in the absence of any phase-transfer catalyst, and a variety of reactive functional groups are tolerated.

Journal Article↗
PubMed1997

Photochemical Reactions of Mesityl Azide with Tetracyanoethylene: Competitive Trapping of Singlet Nitrene and Didehydroazepine.

Irradiation of the title azide 4 in the presence of TCNE gives a mixture of two stable adducts. One of them is identified as the azomethine ylide 5, the structure of which is strictly determined by X-ray crystallography. The other is spectroscopically assigned to the spiroazepine 6. The effect of wavelength of the light employed in the photolysis reveals that the TCNE-4 charge-transfer complex (lambda(max) 454 and 550 nm in dichloromethane) does not participate in the adduct formation. The ratio of the adducts obtained in the photolysis is dependent linearly upon the initial concentration of TCNE, which strongly suggests that the adducts 5 and 6 are produced by competitive trapping of singlet mesitylnitrene (8S) and trimethyldidehydroazepine (9), respectively. The rate constant for the reaction of 8S with TCNE is estimated to be on the order of 10(9) M(-)(1) s(-)(1) or greater. The PM3 calculation indicates that the azomethine ylide 5 is thermodynamically more stable than the aziridine 7, which is thought to be initially formed by the reaction of 8S with TCNE. Thus, we propose that these findings make the first example of competitive trapping of singlet arylnitrene and its ring-expanded isomer with an alkene, which definitely reveals the intervention of singlet nitrene in the photolysis of an aryl azide.

Journal Article↗
PubMed2005

Vibrational relaxation of azide in formamide reverse micelles.

Static and ultrafast infrared spectroscopy have been used to measure absorption spectra and vibrational energy relaxation (VER) times for the antisymmetric stretching vibrational band of azide, N(3)(-), in formamide-containing reverse micelles (RMs). RMs were formed in n-heptane using the surfactant AOT, sodium bis(2-ethylhexyl) sulfosuccinate. The VER times were found to be significantly longer than in bulk formamide. The VER times became longer as the molar ratio of formamide to AOT, omega(F), was decreased. Decreasing omega(F) also resulted in substantial blue shifts of the azide static absorption band compared to the frequency in bulk formamide. The omega(F) dependent studies are consistent with expected size trends, where a larger RM results in more bulklike polar solvent and faster VER rates. These results are in contrast to aqueous AOT RMs where VER times were indistinguishable from those in the bulk and the static spectral shifts were much smaller. The differences between the static and dynamic behavior in aqueous and formamide RMs are related to differences in structural changes upon confinement in RMs.

Journal Article↗
PubMed2003

Epoxide-initiated electrophilic cyclization of azides: a novel route for the stereoselective construction of azabicyclic ring systems and total synthesis of (+/-)-indolizidine 167B and 209D.

[reaction: see text] A novel and general method for the stereoselective construction of 5-hydroxymethyl azabicyclic ring skeletons based on epoxide initiated electrophilic cyclization of azides has been developed and applied in the synthesis of (+/-)-indolizidine 167B and 209D with an overall yield of 16.5% and 17.8%, respectively. The efficiency of this methodology is further exemplified in the synthesis of azepine skeleton via tandem cation-olefin-azide cyclization.

Journal Article↗
PubMed2003

Conversion of aryl azides to O-alkyl imidates via modified Staudinger ligation.

[reaction: see text] o-Carboalkoxy triarylphosphines are shown to react with aryl azides to provide Staudinger ligation products bearing O-alkyl imidate linkages. This is in contrast to alkyl azides whose ligation to o-carboalkoxy triarylphosphines has been reported to yield amide-linked materials. This extension of the Staudinger ligation for coupling of abiotic reagents under biocompatible conditions highlights the utility of commercially available triarylphosphines through which suitable linkers can be attached via an ester moiety.

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PubMed2005

Highly diastereoselective allylic azide formation and isomerization. Synthesis of 3(2'-amino)-beta-lactams.

The stereoselective anti SN2' attack of NaN3 to 3-alkenyl-3-bromo-azetidin-2-ones gave a mixture of diastereomeric azides in fast equilibrium. The [3,3]-sigmatropic rearrangement of allylic azides occurred with complete stereocontrol, allowing the equilibrium to be directed preferentially toward the (E)- or (Z)-isomer, useful precursors of 3(2'-amino)-beta-lactams. [reaction: see text]

Allyl Compounds↗
PubMed2005

From azides to nitriles. A novel fast transformation made possible by BrF3.

[reaction: see text]. Various alkyl and aryl azides, readily obtained from halides or alcohols, were transformed into the corresponding nitriles using bromine trifluoride in moderate to good yields. The reaction is general and gives positive results with aliphatic, aromatic, cyclic, and functionalized azides. It can also be applied to the synthesis of optically active nitriles.

Journal Article↗
PubMed2006

Regioselective trapping of terminal di-, tri-, and tetraynes with benzyl azide.

[Structure: see text] The reaction of benzyl azide with terminal di-, tri-, and tetraynes appended with a range of functional groups has been explored. Standard reaction conditions for BnN3 catalyzed by CuSO4.5H2O gave alkynyl, butadiynyl, and hexatriynyl triazoles in moderate to good yields. The reaction proceeds regioselectively as determined by the X-ray crystallographic analysis of three derivatives (1c, 1d, and 3c), and no evidence of multiple azide addition to the polyyne framework is observed.

Journal Article↗
PubMed2000

Reduction of azides to amines mediated by tin bis(1,2-benzenedithiolate)

[reaction: see text] A procedure for the conversion of azides to amines, which uses NaBH4 and catalytic amounts of tin(IV) 1,2-benzenedithiolate, is disclosed. Primary, secondary, tertiary, aromatic, and heteroaromatic azides are reduced in excellent yields under very mild conditions.

Journal Article↗
PubMed2004

Photocatalytic reduction of aromatic azides to amines using CdS and CdSe nanoparticles.

We have shown that CdS and CdSe nanoparticles can act as very efficient and highly chemoselective photocatalysts for the reduction of aromatic azides to aromatic amines. In several cases, the reaction proceeds with quantum yields near 0.5, which approaches the theoretical maximum for a two-electron process. The wide scope of the reaction was confirmed with compounds containing electron withdrawing (-NO(2), CO(2)R, COR) and electron donating groups (-OMe, -R, -Cl) at the para-, meta-, and ortho-positions. Remarkably, the reaction is relatively insensitive to the electron demands of the substituent. However, azides with meta-substituents give slightly lower yields than those with the same substituent at the ortho- or para-position.

Journal Article↗
PubMed2004

Synthesis of 11C-labelled N,N'-diphenylurea and ethyl phenylcarbamate by a rhodium-promoted carbonylation via [11C]isocyanatobenzene using phenyl azide and [11C]carbon monoxide.

The reaction with phenyl azide and [11C]carbon monoxide to give N,N'-diphenyl[11C]urea and ethyl phenyl[11C]carbamate has been studied with the aim of development of a new methodology for carbonylation using [11C]carbon monoxide with high specific radioactivity. The synthesis of 11C-labelled N,N'-diphenylurea from phenyl azide and [11C]carbon monoxide, with 1,2-bis(diphenylphosphino)ethane-bound Rh(I) complex at 120 degrees C at a pressure of 35 MPa in the presence of aniline was accomplished in 82% trapping efficiency and 82% conversion yield. This approach was also useful for the synthesis of ethyl phenyl[11C]carbamate with lithium ethoxide as a nucleophilic reagent giving 90% trapping efficiency and 76% conversion yield. These reactions can be considered to proceed via a [11C]isocyanate or a [11C]isocyanate-coordinated Rh complex to give the corresponding 11C-products. This protocol provides the chemical basis for the synthesis of [11C]urea and [11C]carbamate derived from [11C]isocyanates.

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