The C=C Bond Decomposition Initiated by Enamine‐Azide Cycloaddition for Catalyst‐ and Additive‐Free Synthesis of N‐Sulfonyl Amidines

Abstract

The chemo-selective synthesis of Nsulfonyl amidines is realized via the decomposition of the enamine C=C bond of enaminoesters through an in situ generated triazoline intermediate. Control experiments prove that the electron withdrawing ester group in the enamine component is crucial in inducing the chemo-selective formation of amidines. The method is featured with high efficiency and sustainability by employing pure water as medium without requiring any catalyst or additive. Scheme 1. Different reaction pathways between enamines/ enamine precursors and azide.

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

“…Beside the proposed aerobic photoredox mechanism, 7 a plausible alternative mechanism was therefore proposed according to the experimental observations discussed above and previously reported literatures. 5,7,13,14 This mechanism comprises two processes: the anaerobic ruthenium-promoted photoredox SET dehydrogenation process to form enamine intermediate; and the cycloaddition and ring-opening decomposition process facilitated by aerobic ruthenium photocatalysis to afford the nal amidine product (Scheme 3). Initially, SET oxidation of amine 2a by the excited state *Ru n produced via photoexcitation of the higher valent ruthenium catalyst forms tertiary amine radical cation A, 7 along with the reduced ruthenium species Ru nÀ1 , which undergoes another SET process with the azide TsN 3 , giving azide radical anion B 5c, 13 and closing the ruthenium catalytic cycle.…”

“… 5,7 The yield of 4q significantly declined when this transformation took place in the absence of oxygen (entry 2), confirming the crucial role of oxygen in the cycloaddition and decomposition process which is suggested by the results of control experiments shown in Table 4 . However, only trace amount of amidine 4q could be observed on TLC when the reaction was conducted in the absence of the ruthenium photocatalyst or without visible-light irradiation (entries 3–6), demonstrating that the cycloaddition and decomposition process, although it might occur spontaneously with a extremely low rate (entry 6), 14 could be considerably facilitated by aerobic ruthenium photocatalysis (entry 1).…”

“…Eventually, 1,3-dipolar addition of enamine 1a with tosyl azide 3a engenders a triazoline intermediate E, followed by decomposition of triazoline E to release diazomethane F, 14 along with the final amidine product 4a, which might undergo oxidative dealkylation 11 to generated the de-ethylated byproduct 5b. Results shown in Table 5 indicated that such cycloaddition-decomposition process, which might take place spontaneously albeit in very low efficiency (entry 6), could be promoted by aerobic ruthenium photocatalysis (entry 1).…”

Recent Advances in Reactions Using Enaminone in Water or Aqueous Medium

“…The reactions were performed in the presence of Mn(II) salt in mixed dioxane/water medium. By heating at 100 °C, the thermo-induced homo-cleavage of peroxide donated carboxyl free radical In addition, our group [40] Notably, based on the inspiration of the above method in the synthesis of N-sulfonyl amidines 69 and 71. We [41] later successfully developed a method for the synthesis of α-diazoketones 73 by reacting enaminones 26 and methyl sulfonyl azide 72 in water with microwave irradiation.…”

ZIF‐8 Catalysed Efficient Synthesis of Dicyano Alkyl Quinoline Derivatives in Aqueous Medium

“…Conversely, the alternate for volatile and toxic organic solvents by eco‐ and user‐friendly solvents were great value as per green chemistry principles . It is well known that water‐mediated chemical reactions were highly preferable owing to their inexpensive, simple to operate, economically viable, and environmental benign applications . Therefore, the preparation of 2‐alkylquinoline derivatives in the aqueous medium is always very significant in synthetic organic chemistry.…”