A Remarkable Accelerating Effect of Ag-Salt on Intramolecular Cyclization of o-(1-Alkynyl)benzenesulfonamides

Abstract

Herein, we report transition metal-catalyzed intramolecular cyclization of o-(1-alkynyl)benzenesulfonamides to afford 3-substituted benzothiazines regioselectively via a C-N bond forming reaction and Cu-catalyzed sequential C-N and C-C bond formation leading to the corresponding 3,4-disubstituted derivatives.

Palladium-Catalyzed Alkynylation of Aryl and Hetaryl Halides: A Journey from Conventional Palladium Complexes or Salts to Palladium/Carbon

“…The transition-metal-catalyzed intramolecular cyclization of 2-alkynylbenzenesulfonamides 33 was explored for this purpose, and the use of silver(I) hexafluoroantimonate was found to be highly effective, as the reaction was completed within a few minutes to afford dioxides 39 in excellent yields (Table 19). 66 The use of copper salts was also explored for the cyclization of 33, and copper(I) iodide provided the best results, although the reaction required a higher temperature and a longer reaction time compared to when silver(I) hexafluoroantimonate is used (Table 20). 66 Nevertheless, the present silver-and copper-mediated cyclization of 33 In further continuation of the investigations of palladiumcatalyzed alkynylation of a-halo enones of the type -CO-C(X)=CR-, e.g.…”

“…66 The use of copper salts was also explored for the cyclization of 33, and copper(I) iodide provided the best results, although the reaction required a higher temperature and a longer reaction time compared to when silver(I) hexafluoroantimonate is used (Table 20). 66 Nevertheless, the present silver-and copper-mediated cyclization of 33 In further continuation of the investigations of palladiumcatalyzed alkynylation of a-halo enones of the type -CO-C(X)=CR-, e.g. 3-halo(thio)flavones, particularly under copper-free conditions, it was observed that alkynyl or enynyl derivatives (isolated when R = aryl) were not formed when R = H. The product isolated was identified as a substituted benzene derivative, confirmed by spectral and single-crystal X-ray crystallographic data.…”

AgNO3 mediated C–N bond forming reaction: synthesis of 3-substituted benzothiazines as potential COX inhibitors

“…To overcome this problem a direct synthesis of benzothiazine derivatives was developed that involved intramolecular cyclization of o-(1-alkynyl)benzenesulfonamides in the presence of AgSbF 6 and Et 3 N. 11 While this reaction was found to be highly regioselective and afforded good to excellent yields of desired products the methodology, however, involved the use of relatively expensive and corrosive AgSbF 6 catalyst. As part of our continuing effort on the identification of biologically active small organic molecules we required a library of benzothiazine derivatives for various in vitro pharmacological screens.…”

“…12 The synthesis of our key starting material o-(1-alkynyl)benzenesulfonamides (1) was carried out via the Pd/C mediated coupling of o-iodobenzenesulfonamide (3) with terminal alkynes in good yields (Scheme 2). 10,11 The required sulfonamide (3) was prepared either via treating 2-iodobenzenesulfonyl chloride 13 with MeNH 2 in dioxane/THF 14 or iodination of N-methyl benzene sulfonamide derivative 15 using n-BuLi in THF according to the literature. 10 To establish the optimized reaction conditions we examined the AgNO 3 mediated intramolecular cyclization of N-methyl-2-ptoluylethynyl benzenesulfonamide (1a) under various conditions (Table 1).…”

(PPh3)AuCl/AgOTf-Catalyzed Intermolecular Hydroamination of Alkynes with Sulfonamides To Form N-Sulfonyl Imines

“…Only trace of 3a was formed by using Cu(OTf) 2 which was a robust catalyst in intramolecular hydroamination of alkynylsulfonamides (entry 11). 11b Other metal catalysts such as (PPh 3 ) 2 NiCl 2 , (PPh 3 ) 2 PdCl 2 , and (cod)PtCl 2 were ineffective (entries [12][13][14]. Different solvents were screened and toluene was found to be the most suitable one.…”