Strong Closed-Shell Interactions in Inorganic Chemistry.

Synthetic Methods for Compounds Having CF3–S Units on Carbon by Trifluoromethylation, Trifluoromethylthiolation, Triflylation, and Related Reactions

The research on 1,2,3-triazoles has been lively and ever-growing since its stimulation by the advent of click chemistry The attractiveness of 1H-1,2,3-triazoles and their derivatives originates from their unique combination of facile accessibility via click chemistry and truly diverse supramolecular interactions, which enabled myriads of applications in supramolecular and coordination chemistry The nitrogen-rich triazole features a highly polarized carbon atom allowing the complexation of anions by hydrogen and halogen bonding or, in the case of the triazolium salts, via charge-assisted hydrogen and halogen bonds On the other hand, the triazole offers several N-coordination modes including coordination via anionic and cationic nitrogen donors of triazolate and triazolium ions, respectively After CH-deprotonation of the triazole and the triazolium, powerful carbanionic and mesoionic carbene donors, respectively, are available The latter coordination mode even features non-innocent ligand behavior Moreover, these supramolecular interactions can be combined, eg, in ion-pair recognition, preorganization by intramolecular hydrogen bond donation and acceptance, and in bimetallic complexes Ultimately, by clicking two building blocks into place, the triazole emerges as a most versatile functional unit allowing very successful applications, eg, in anion recognition, catalysis, and photochemistry, thus going far beyond the original purpose of click chemistry It is the intention of this review to provide a detailed analysis of the various supramolecular interactions of triazoles in comparison to established functional units, which may serve as guidelines for further applications

Beyond click chemistry - supramolecular interactions of 1,2,3-triazoles.

(Chemical Equation Presented) 4-Substituted 1-(N-sulfonyl)-1,2,3-triazoles are selectively obtained by using the Cu-catalyzed azide-alkyne cycloaddition reaction with sulfonyl azides. Performing the reaction at 0°C in chloroform in the presence of 2,6-lutidine and Cul as the catalyst effectively prevents the ketenimine pathway and provides convenient access to N-sulfonyltriazoles in good to excellent yields.

Copper‐Catalyzed Synthesis of N‐Sulfonyl‐1,2,3‐triazoles: Controlling Selectivity

Rhodium-stabilized carbenes possess diverse reactivity in a variety of organic transformations, such as addition to C–C and C–heteroatom multiple bonds, insertion into C–H and C–heteroatom bonds, as well as ylide formation.[1] However, this powerful chemistry is mostly limited to rhodium carbenes derived from the corresponding diazo compounds. Obviously, development of new and efficient methods to access Rh carbenoids from alternative and stable precursors could expand the scope of this chemistry.

It is known that the stability of the 1,2,3-triazole ring is affected by the substituents at the N1, C4, and C5 atoms of the heterocycle.[2] For example, triazoles 1 that bear a sulfonyl group at the N1 atom exist in equilibrium with diazoimine tautomer 2.[3] Gevorgyan and Fokin took advantage of this process by trapping diazoimine 2 with a RhII catalyst to produce the putative RhII–iminocarbene 3 (Scheme 1).[4] This intermediate possessed reactivity inherent for RhII carbenoids. For example, it reacted with alkenes to form cyclopropane derivatives 4.[4] Later, this process was performed by Fokin and co-workers in a highly enantioselective manner.[5] On the other hand, the presence of the imino group at the α-position of 3 opens opportunities for novel heterocyclizations. Thus, the transannulation[6] reaction of N-sulfonyl triazoles with nitriles produced imidazoles 5,[4] whereas the reaction with alkynes[7a] led to pyrroles 6.[7b] As shown by Fokin and co-workers, Rh–iminocarbene 3 could also undergo insertion into a secondary or tertiary C–H bond of alkanes (as a solvent) to produce valuable β-chiral amines 7 in high yields and enantioselectivities.[8a] In 2012, Murakami reported an efficient RhII-catalyzed hydration of triazoles 1 to form α-aminoketones 8, proceeding through insertion of the RhII–iminocarbene intermediate into the O–H bond of water.[8b] Shortly after, Fokin and co-workers disclosed the RhII-catalyzed reaction of N-sulfonyl triazoles 1 with arylboronic acids, thus stereoselectively furnishing enamines 9.[8c] Note-worthy, the N-sulfonyl triazole precursors are easily available by Cu-catalyzed alkyne–azide cycloaddition (CuAAc) reaction,[9] which makes this approach to Rh-stabilized carbenes attractive for the synthesis of valuable carbo- and heterocyclic molecules (Scheme 1).



Scheme 1

Use of N-sulfonyl triazole to form Rh–iminocarbene.



Very recently, the groups of Murakami[10] and Fokin[11] independently reported the RhII-catalyzed denitrogenative rearrangement of 1-(N-sulfonyl-triazol-4-yl)alkanols 10, proceeding through migration of different groups to the Rh–carbene center of 12. The subsequent elimination of rhodium from the 12 produces iminoenol 14, which is converted to Z-substituted enaminone 11 upon facile proton transfer (Scheme 2).



Scheme 2

The RhII-catalyzed rearrangement of triazolyl alcohols. Conditions A (Miura and Murakami[10]): CHCl3, 140°C, microwave, 15 min. Conditions B (Fokin[11]): CHCl3, 70°C, 5–60 min. Oct=octanoate, Ts=4-toluenesulfonyl.



In general, the migratory aptitude of different groups to the Rh–carbene center derived from a diazo compound follows the common tendency: hydride > phenyl > primary alkyl > secondary alkyl groups.[12] Likewise, in the transformation 12→13, the 1,2-migration of hydride is favored over the 1,2-shift of alkyl and phenyl groups (Table 1, entries 1 and 2, respectively). The phenyl group, in turn, migrates more easily than the methyl group (entry 3), whereas the methyl group migrates more easily than the isopropyl group (entry 4). Furthermore, cyclic 1-triazolylalkanols 10 f underwent efficient ring expansion to produce the corresponding cyclic enaminones 11 f (entries 7 and 8). The reaction of fluorenol derivative 10g led almost quantitatively to the corresponding hydroxyphenanthrene derivative 11 g (entries 9 and 10). In most cases, a predominant formation of the Z-stereoisomer was observed, which can be attributed to the concerted transformation 14→11 (kinetic control), and to the higher stability of the Z-stereoisomer as a result of an additional stabilization through intramolecular hydrogen bonding (thermodynamic control).



Table 1

Migrations of different groups to the metal–carbene center of RhII–iminocarbenes (see Scheme 2).



Interestingly, protection of the hydroxy group as acetate enabled its selective migration to the carbene center to form products 16 (entry 11). It was also shown that 4-cyclohexyl and 4-tert-butyl triazoles gave the products of hydride and methyl group migration (18a and 18b, respectively) under these reaction conditions (entries 12 and 13). Moreover, Fokin and co-workers reported the first example of amine migration to the RhII carbenoid center. Thus, the reaction of 4-alkylamino triazole 17c produced the corresponding enamine 18c in good yields (entry 14).[11]

In conclusion, the RhII–iminocarbenes, derived from the corresponding N-sulfonyl 1,2,3-triazoles, could be used in several transformations inherent for metal carbenoids. Thus, cyclopropanation of alkenes, reactions with alkynes, nitriles, and boronic acids, as well as insertion into C–H and O–H bonds were impressively developed. In addition, the recent reports also disclosed migrations of different groups to the RhII–carbene center of imino carbenoids. The N-sulfonyl 1,2,3-triazole precursors are easily available by CuAAc reaction of alkynes with azides, which makes this approach very useful for straightforward generation of RhII carbenoids. Some transformations could even be efficiently performed in a one-pot manner starting from alkynes and sulfonyl azides. Therefore, the reactivity of RhII–iminocarbenes can be tuned easily by variation of substituents in the parent triazole through the simple CuAAc approach. Moreover, a natural low concentration of diazoimine, which exists in equilibrium with triazoles, maintains a low concentration of the reactive RhII carbenoid, which obviates the necessity of slow-addition techniques that are often required in the reactions of diazo compounds.

Versatile Reactivity of Rhodium–Iminocarbenes Derived from N-Sulfonyl Triazoles†

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 1473. DOI:10.1002/anie.198214730

Intramolecular Diels‐Alder Reaction of Allenecarboxanilides

Durch Umsetzung von Lithiumacetyliden 1 mit Trialkyl- und Triphenylmetallhalogeniden 2 werden (Silylathinyl)-, (Germylathinyl)- und (Stannylathinyl)amine 3 synthetisiert. Diese Inamine addieren Aryl- und Sulfonylazide zu den 5-Amino-1,2,3-triazolen 4,5 und 7, die im Falle der Sulfonyladdukte (5 und 7)weitgehend zu den Diazoacetamidinen 6 bzw. 8 isomerisieren. Die Diazoverbindungen 8 spalten den Metallrest bei Einwirkung von Wasser oder Deuteriumoxid leicht ab unter Bildung der [2-H1]- und der [2-D1]Diazoacetamidine 9 und 10.



Investigations on Diazo Compounds and Azides, XXV1) Azide Additions on (Silylethynyl)-, (Germylethynyl)- and (Stannylethynyl)amines



The lithium acetylides 1 react with trialkyl- and triphenylmetal halides 2 to form the (silylethynyl)-, (germylethynyl)-, and (stannylethynyl)amines 3. The ynamines add aryl-and sulfonyl azides to the 5-amino-1, 2,3-triazoles 4,5, and 7, which in the case of the sulfonyl azide adducts 5 and 7 isomerize largely to the diazoacetamidines 6 and 8, respectively. Water or deuterium oxide hydrolyze the carbon-metal bond of the diazo compounds 8 with formation of the [2-H1] - and [2-D1]diazoacetamidines 9 and 10.

Untersuchungen an Diazoverbindungen und Aziden, XXV1) Azid‐Additionen an (Silyäthinyl)‐, (Germyläthinyl)‐ und (Stannyläthinyl)amine

Das vollstandige Manuskript dieser Zuschrift erscheint in: Angew. Chem. Suppl. 1982, 1473. DOI: 10.1002/ange.198214730

Intramolekulare Diels‐Alder‐Reaktion von Allencarboxaniliden

Die Umsetzung der βH-Inamine 3a–f mit Sulfonylaziden spielt sich ausschlieslich im Sinne einer Diazogruppen-Ubertragung zu den Guanyldiazomethanen 6a–u ab, wobei die isomeren Triazole 5 als Zwischenstufen durchlaufen werden Lediglich die Reaktion von 3f mit 4-Dimethylamino-benzolsulfonsaureazid liefert 5-Diphenylamino-l-[4-dimethylamino-benzolsulfonyl]-123-triazol, das in Chloroform-Losung mit dem Diazo-Isomeren im Gleichgewicht steht Die Reaktivitat der Guanyldiazomethane wurde nur orientierend untersucht: Mit ather Chlorwasserstoff entstehen die Chloracetamidine 7a–h, mit Diacylacetylenen die Cycloaddukte 8a–c und mit Triphenylphosphin die Phosphazine 9a–e



Studies with Diazo Compounds and Azides, XIV Guanyldiazomethanes by Diazo Group Transfer with βH-Ynamines



The reaction of the βH-ynamines 3a–f with sulfonyl azides occurs exclusively in the sense of a diazo group transfer, leading to the guanyldiazomethanes 6a–u, whereby the isomeric triazoles are intermediates Only the reaction of 3f with 4-(dimethylamino)benzenesulfonic acid azide yields 1- [4-( dimethylamino)benzenesulfonyl]-5-( diphenylamino )-123-triazole, which exists in equilbrium with the diazo isomer in chloroform solution A limited investigation of the reactivity of the guanyldiazomethanes was performed: With etherial hydrogen chloride the chloroacetamidines 7a–h are formed, diacylacetylenes yield the cycloadducts 8a–c and triphenylphosphine yields the phosphazines 9a–e

Untersuchungen an Diazoverbindungen und Aziden, XIV. Guanyldiazomethane durch Diazogruppen‐Übertragung auf βH‐Inamine

Die in ω-Position unsubstituierten 2,3-Butadienanilide 6a–h werden auf dem Inaminweg synthetisiert und der Thermolyse unterworfen. Sie isomerisieren ohne Ausnahme in einer intramolekularen Diels-Alder-Reaktion mehr oder weniger rasch, irreversibel und quantitativ zu den tricyclischen Lactamen 8a–h, wobei der Anilinkern jeweils als „Dien” fungiert. Die Strukturen 8 werden spektroskopisch und durch eine Rontgenstrukturanalyse (8b) bestatigt.

Gerhard Himbert

Papers

Intramolecular Diels‐Alder Reaction of Allenecarboxanilides

Untersuchungen an Diazoverbindungen und Aziden, XXV1) Azid‐Additionen an (Silyäthinyl)‐, (Germyläthinyl)‐ und (Stannyläthinyl)amine

Intramolekulare Diels‐Alder‐Reaktion von Allencarboxaniliden

Untersuchungen an Diazoverbindungen und Aziden, XIV. Guanyldiazomethane durch Diazogruppen‐Übertragung auf βH‐Inamine

Cycloadditionen, 6. Intramolekulare Diels-Alder-Reaktion bei Allencarboxaniliden; Variation des zur Carboxamidgruppe geminal stehenden Restes