Reactions of Sulfonyl Azides

Copper-Catalyzed Reactions with Other Dipolar Spedes 

In the mechanism of the CuAAC reaction described above, the metal catalyst activates terminal alkyne for reaction with a Cu-coordinated azide. This mode of reactivity operates with other dipolar reagents as well. In fact, the first example of a copper-catalzyed 1,3-dipolar cycloaddition reaction of alkynes was reported for nitriones by Kinugasa in 1972 [124]. An asymmetric version of the Kinugasa reaction was developed by Fu et al. in 2002 [125, 126]. 

In contrast, Cu(I) catalysis makes possible the efficient synthesis of 3,5-disubstituted isoxazoles 57 from aromatic or aliphatic aldehydes and alkynes. Stable nitrile oxides can be isolated and subsequently submitted to the reaction 

Reactions of azomethine imines with alkynes catalyzed by copper yielding fused nitrogen heterocycles have also been reported [131]. 

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A mixture of sulfonyl-azafulleroid 168 and sulfonylaziridino-fullerene 169 was obtained by reaction of sulfonyl azide with CgQ in o-dichlorobenzene at 160 °C (Scheme 4.30) [173]. The ratio of the two products depends on the substituent of the sulfonyl group. In all cases the aziridino fullerene can be obtained from the azafulleroids by irradiation. 

The importance of a-diazo ketones as synthetic intermediates has led to the development of a number of general methods for their preparation.5 Particularly popular approaches include the acylation of diazo alkanes and the base-catalyzed "diazo group transfer" reaction of sulfonyl azides with 8-dicarbonyl compounds.6-7 While direct diazo transfer to ketone enolates is usually not a feasible process,8-9 diazo transfer to simple ketones can be achieved in two steps by employing an indirect deformylative diazo transfer strategy in which the ketone is first formylated under Claisen condensation conditions, and then treated with a sulfonyl azide reagent such as p-toluenesulfonyl azide.6a,6c,9,i0,11... 

Two reactions of sulfonyl azides show promise in the preparation of u-triazole amino carboxamides (Eq. 18) and nitriles (Eq. 19). ... 

The reaction of sulfonyl azides with terminal alkynes is an interesting exception. Whereas aryl and alkyl azides react with activated alkynes to give the corresponding 1,2,3-triazoles, intermediate sulfonyltriazoles result in the formation of different products. In the presence of amines, N-sulfonyl azides are converted to M-sulfonyl amidines, whereas under aqueous conditions, M-acylsulfonamides are the major products [76-78]. Nevertheless, Fokin et al. reported conditions for the successful formation of N -sulfonyl-1,2,3-triazoles 105 shown in Scheme 22 [79]. 

Namitharan, K. and Pitchumani, K. 2011. Copper(l)-catalyzed three component reaction of sulfonyl azide, alkyne, and nitrone cycloaddition/rearrangement cascades A novel one-step synthesis of imidazolidin-4-ones. Org. Lett. 13(21) 5728-5731. 

S. Chang, J. Org. Chem. 2008, 73, 5520-5528. Mechanistic studies on the Cu-catalyzed three-component reactions of sulfonyl azides, 1-alkynes and amines, alcohols, or water dichotomy via a common pathway. 

One popular method in the synthesis of a-diazo ketones is in the base-catalyzed diazo group transfer reaction of sulfonyl azides with activated dicarbonyl compounds The Regitz Diazo Reaction) While direct diazo transfer to ketone enolates is usually not feasible, a two step deformylative diazo transfer strategy has been employed, whereby a ketone is first... 

A novel and efficient approach to 4-sulfonamidoquinolines catalyzed by Cul via a cascade reaction of sulfonyl azides with alkynyl imines has been developed by Cheng and Cui (Scheme 8.87). The reaction process includes 1,3-dipole cycloaddition/ketenimine formation/6 r-electrocyclization/[l,3]-H shift. Various 4-sulfonamidoquinolines were afforded in moderate to good yields under this mild copper catalytic system [157]. 

Wang et al. developed a mild and efficient procedure for the synthesis of substituted iminocoumarin derivatives through a multicomponent reaction of sulfonyl azides, terminal alkynes, and salicylaldehydes (Scheme 8.118). The CuI/EtgN catalytic system could give the desired products iminocoumarin in good to excellent yields. The C(sp)-H could be activated via the formation of ketenimine species in this transformation [193]. 

SCHEME 5.57 Cu(I)-catalyzed three-component cascade reaction of sulfonyl azides, terminal alkynes, and nucleophiles. 

SCHEME 5.62 Four-component reactions of sulfonyl azides with terminal alkynes, alcohols, and nitroalkenes or Baylis-HiUman adducts. 

A cascade reaction involving 1,3-dipolar cycloaddition of ketenimine was reported by Li et al. [69], The transformation combines a CuAAC reaction, a Lewis add-catalyzed 6-endo cyclization of Af -(2-alkynylbenzylidene)hydrazide, a [2+3] cycloaddition, and an aromatization in a single step to afford 2-amino-//-pyrazolo[5,l-a] isoquinolines 102 in good to excellent yields (Schane 5.66). The copper-catalyzed three-component reaction of sulfonyl azides, alkynes, and nitrones also involves 1,3-dipolar cycloaddition between ketenimine and nitrone (Scheme 5.67) [70]. The nitrone substrates in this transformation could be generated in situ from benzalde-hydes and hydroxylamines. 

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