Photoinduced Cascade Reaction of Tertiary Amines with Sulfonyl Azides: Synthesis of Amidine Derivatives

Abstract

A metal-free cascade reaction of tertiary amines with sulfonyl azides promoted by acridinium salts under blue light irradiation was developed and provided amidine derivatives in moderate to good yields. Enamine was generated from tertiary amine via single-electron transfer promoted by acridinium salts, and the following [3 + 2] cyclization with sulfonyl azide and CH 2 N 2 release afforded the desired products.

Transition metal- and catalyst-free one-pot green method for the synthesis of N-sulfonyl amidines via direct reaction of sulfonyl azides with amines

“…19 On the other hand, Li and co-workers reported the cascade reaction of tertiary amines with sulfonyl azides in the presence of DEAD (diethyl azodicarboxylate) for the preparation of N-sulfonyl amidines. 20 Recently, photocatalyzed cross-coupling of arylsulfonyl azides with tertiary amines in the presence of eosin Y and acridinium salts have been reported by Zeng et al 21 and Pan et al 22 respectively. An electrochemical synthesis of N-sulfonyl amidines from aliphatic amines and sulfonyl azides has been reported by Wang, Du and Zah.…”

Visible-light enabled room-temperature dealkylative imidation of secondary and tertiary amines promoted by aerobic ruthenium catalysis

“…It has also been demonstrated that such SET process can be facilitated by the ruthenium catalyst without oxygen, due to the amount of 5a acquired in entry 2 that indicated most of 2a could be converted to the enamine intermediate 1a with the assistance of the ruthenium catalyst in the absence of oxygen. On the contrary, it seems that oxygen cannot promote the spontaneous formation of enamine 1a (entry 3), and the previously proposed aerobic photocatalysis pathway 7 seems to contribute little in this ruthenium-promoted visible-light induced imidation, since the yield of 5a indicated that most of 1a was engendered through the above anaerobic SET process even in aerobic environment (entry 1). According to the above observations, it could be concluded that oxygen might be unnecessary to the conversion from amine 2a to enamine 1a, while it might enhance the following cycloaddition and ring-opening decomposition process, comparing the yields of 4a in entries 1 and 2.…”

“…Furthermore, the spontaneity of this visible-light enabled imidation in the absence of oxygen and photocatalyst (entry 13, Table 1 ) attracted our attentions, for such observation suggested that an anaerobic pathways to realize this imidation probably coexist with the aerobic photoredox pathway proposed by Zeng and Pan, 7 where oxygen was proposed to serve a vital role in dehydrogenation. To gain more insights into the mechanistic picture, some control experiments were conducted, especially focusing on identification of byproducts generated along with the amidine product ( Table 4 ).…”

“…Our attention was then emphasized on other means beside electrochemical oxidation for the SET oxidation to generate nitrogen-centred radical cation that initiates such dealkylative imidation, and photoredox catalysis 6 which provides a potent synthetic strategy at room temperature and ambient pressure is considered to be the most efficient and green solution. Recently, Zeng 7 a and Pan 7 b disclosed two separate studies on visible-light-induced sulfonylimidation of tertiary amine using Eosin Y and acridinium salt, respectively, as organic photocatalysts in air ( Scheme 1c ), 7 based on an earlier report in which it had been proved that enamine 1 can be engendered from tertiary amine through photocatalysis. 8 However, employing secondary amine, such as diethylamine, instead of tertiary amine afforded sulfonylated diethylamine 7 a rather than the amidine product.…”

Recent Advances in Photocatalytic C–N Bond Coupling Reactions

“…Tertiary amines were effectively coupled with sulfonyl azides to give amidine derivatives (Scheme 83). 86 SET to the excited photocatalyst would generate a tertiary amine radical cation. Subsequent hydrogen radical abstraction by an oxygen radical anion and a double bond shift results in the formation of an enamine intermediate.…”