Rh(II)-Catalyzed Transannulation of 1,2,4-Oxadiazole Derivatives with 1-Sulfonyl-1,2,3-triazoles: Regioselective Synthesis of 5-Sulfonamidoimidazoles

Abstract

An effective method for the synthesis of fully substituted 5-sulfonamidoimidazoles by Rh(II)-catalyzed transannulation of 1,2,4-oxadiazole derivatives with N-sulfonyl-1,2,3-triazoles is reported. The reaction works well with both aromatic 1,2,4-oxadiazoles and 1,2,4-oxadiazol-5-ones providing a flexible approach to N-(alkoxy/amino)carbonyl- and N-alkyl-substituted imidazoles. Both the disclosed reactions are completely regioselective and provide the first examples of a carbenoid-mediated transformation of N,N,O-heterocycles.

Recent advances in the synthesis of imidazoles

“…For example, Strelnikova et al reported the synthesis of 5-sulphonamidoimidazoles 35 or 36 from the reaction of two different heterocyclic starting materials in the presence of a rhodium catalyst (Scheme 8). 27 Thus, reaction of 1,2,4-oxadiazole derivatives 33 and 34 with 1-sulphonyl-1,2,3-triazoles 32 at 84°C in DCE afforded the desired imidazoles 35 and 36 in good to excellent yield. In addition to a suphonolated amine at the C-5 position, this protocol produced imidazoles substituted at the N-1 position with either an ester or alkyl moieties.…”

An Efficient Synthesis of Functionalized 2H-1,3,5-Oxadiazines via Metal-Carbenoid-Induced 1,2,4-Oxadiazole Ring Cleavage

“…8b,10 In particular, the only known example of a metallocarbenoid-mediated opening of the 1,2,4-oxadiazole ring is the reaction with rhodium azavinyl carbenoids leading to 1,5-cyclization productsimidazole derivatives. 11 At the same time, the accessibility of a large number of 1,2,4-oxadiazoles and availability of convenient methods for their structural modification make them attractive starting materials for synthetic practice. 12,13 The reactions with nucleophiles are characteristic of these compounds, while reactions with electrophilic reagents, are much less common.…”

“…Aryl-, benzoyl-, and tosyl-substituted -diazoacetic esters 2c-f as well as 3-diazopentane-2,4-dione (2j) were decomposed by both Rh 2 (OAc) 4 and Rh 2 (Piv) 4 without any conversion of oxadiazole 1a (Table 1, entries [3][4][5][6][7][8][9][10][11][12][13][14][15][16]12). The reason for the failure is probably the low nucleophilicity of the oxadiazole.…”

Assembly of 5‐Aminoimidazoles via Palladium‐Catalysed Double Isocyanide Insertion Reaction

“…Among functionally substituted imidazole derivatives, 5‐aminoimidazoles have attracted increased attention owing to their excellent biological activities, such as Hsp90 inhibition, [4] adenosine A 2A receptor antagonism [5] and antiplatelet [6] and antimicrobial activities [7] . Accordingly, great efforts have been devoted to the preparation of 5‐aminoimidazole derivatives [6,8–11] . Multistep cascade reaction (Scheme 1a), [8] microwave‐assisted multicomponent domino cyclisation (Scheme 1b) [9] and Rh‐catalysed transannulation of 1,2,4‐oxadiazoles with 1‐sulfonyl‐1,2,3‐triazoles (Scheme 1c) are notable examples [10] .…”

“…Accordingly, great efforts have been devoted to the preparation of 5‐aminoimidazole derivatives [6,8–11] . Multistep cascade reaction (Scheme 1a), [8] microwave‐assisted multicomponent domino cyclisation (Scheme 1b) [9] and Rh‐catalysed transannulation of 1,2,4‐oxadiazoles with 1‐sulfonyl‐1,2,3‐triazoles (Scheme 1c) are notable examples [10] . Despite this considerable progress, the syntheses of 5‐aminoimidazoles are largely less developed, and they are often restricted by various drawbacks (e. g., tedious synthetic sequences, harsh synthesis conditions, special starting materials and use of expensive catalysts), which seriously limit their further applications.…”