Cycloaddition of sulfonyl azides and cyanogen azide to enamines. Quantum-chemical calculations concerning the spontaneous rearrangement of the adduct into ring-contracted amidines

Mechanistic Evaluation of Bioorthogonal Decaging with trans-Cyclooctene: The Effect of Fluorine Substituents on Aryl Azide Reactivity and Decaging from the 1,2,3-Triazoline

“…Finally, as part of our investigation we were able to examine the stability of 1,2,3-triazolines (experimentally and computationally), and the subsequent product distribution following degradation of the ring. This adds mechanistic insight into the degradation process, and complements the work of others in this area. ,,,− Due to the importance of the triazoline in organic chemistry, this provides valuable information for synthetic chemists, enabling them to design triazolines of varying stability.…”

“…Triazolines are an important class of compounds used in synthetic chemistry, and there is a significant amount of effort involved in understanding their formation and subsequent degradation mechanisms. ,,,− Therefore, the results obtained in our NMR and HPLC-UV experiments provide an interesting addition to the current mechanistic understanding of triazoline synthesis, stability, and subsequent degradation products. To understand the reason for the instability of the triazoline formed in the case of 1d / 11d relative to the triazolines resulting from the cycloaddition of the nonsubstituted 1a / 11a and other fluoro-substituted analogues 1b , 1c , 1e , and 1f , a mechanistic study was conducted to relate the fluorine substitution to the triazoline degradation and imine hydrolysis.…”

Unexpected Direct Synthesis of N‐Vinyl Amides through Vinyl Azide–Enolate [3+2] Cycloaddition

“…Our calculations additionally indicate that the rearrangement–nitrogen‐extrusion process is likely to be an asynchronous process (see the reaction movie in the Supporting Information); initial protonation leads immediately to the formation of diazonium ion 44 through cleavage of the N−N bond, and 44 then undergoes slower reformation of the carbonyl functionality and a 1,2‐hydride shift to afford vinyl amide 2 . The fundamental mechanistic processes proposed herein also appear to be in broad agreement with a recent computational study on related azide–enamine cycloaddition reactions to give ring‐contracted amidines . The current work does not appear to rule out the possible intermediacy of an aziridine species in these processes.…”

Unexpected Direct Synthesis of N‐Vinyl Amides through Vinyl Azide–Enolate [3+2] Cycloaddition

“…Analogous cycloaddition reactions for phenyl and ethyl azide were also calculated to assess the effects of orbital delocalization on reactivity and facilitate comparison with the literature and our own observations. [20] Thec urrent work does not appear to rule out the possible intermediacyo fa na ziridine species in these processes. [9][10][11] Tr ansition states for three virtual azides leading to the experimentally observed regioisomer,e xemplified by TS1 b leading to 42 b (R = vinyl), were associated with lower activation energies of 2.0-6.1 kcal mol À1 (phenyl TS1 a % vinyl TS1 b < ethyl TS1 c).…”

“…[9a] Our calculations additionally indicate that the rearrangement-nitrogen-extrusion process is likely to be an asynchronous process (see the reaction movie in the Supporting Information);i nitial protonation leads immediately to the formation of diazonium ion 44 through cleavage of the N À Nb ond, and 44 then undergoes slower reformation of the carbonyl functionality and a1 ,2-hydride shift to afford vinyl amide 2.T he fundamental mechanistic processes proposed herein also appear to be in broad agreement with ar ecent computational study on related azide-enamine cycloaddition reactions to give ring-contracted amidines. [20] Thec urrent work does not appear to rule out the possible intermediacyo fa na ziridine species in these processes.…”