Pericyclic versus Pseudopericyclic 1,5-Electrocyclization of Iminodiazomethanes. An ab Initio and Density Functional Theory Study

Abstract

Density functional (B3LYP/6-311+G) and ab initio (MP2/6-311+G and MP4(SDTQ)/6-311+G//MP2/6-311+G) calculations on the ring closure reactions of (E)- and Z-iminodiazomethane ((E)-5, (Z)--5), vinyldiazomethane 7, and formyldiazomethane 9 to 1H-1,2,3-triazole 6, 3H-pyrazole 8, and 1,2,3-oxadiazole 10, respectively, are reported. (E)-5 cyclizes via a low barrier (ca. 10 kcal mol(-)(1)) pseudopericyclic nonrotatory transition state. Ring closure of (Z)-5 and 7 proceeds by a monorotatory movement of the imino or vinyl group with a substantially higher barrier (ca. 25 kcal mol(-)(1)). Despite being endothermic, for the reaction 9 --> 10 also a rather low activation energy (ca. 10 kcal mol(-)(1)) is computed. The NBO analysis is used to interpret the electronic structures of the respective transition states in terms of their pericyclic monorotatory (TS ((Z)-5 --> 6), (TS (7 --> 8)) or pseudopericyclic nonrotatory ((TS ((E)-5 --> 6), (TS (9 --> 10)) nature.

A Theoretical Study of Cyclohexyne Addition to Carbonyl–Cα Bonds: Allowed and Forbidden Electrocyclic and Nonpericyclic Ring-Openings of Strained Cyclobutenes

“…22 Computational investigations have provided evidence that psuedopericyclic transition states are typically planar with no rotation of the terminal π-bonds. For instructive reviews of the subject, the reader is directed to articles of Kappe et al, 23 Birney et al, 24 and references therein. Isomerization of 7a via 8a forms the more stable product 7a ′.…”

Heterociclos 1,2,3-triazólicos: histórico, métodos de preparação, aplicações e atividades farmacológicas

“…Por ex., o 4-carboxiamida-5-metilamino-1,2,3-triazol (50a) quando aquecido a 160 o C rearranja-se, produzindo 5-amino-4-carboxiamida-1-metil-1,2,3-triazol (50b) (Esquema 11) 41 . Recentemente, Fabian e Bakulev 42 utilizando cálculos teóricos confirmaram a proposta de que ocorre uma ciclização pseudopericíclica. Muitos outros trabalhos mostraram que este rearranjo também ocorre em triazóis contendo os substituintes diazometil 43 , amino [43][44][45] .…”

Catalytic Asymmetric Transannulation of NH‐1,2,3‐Triazoles with Olefins

“…[5] Recently, we [6] and others [7] have demonstrated that transition metal azavinyl carbenes can be accessed directly from certain electron-deficient 1,2,3-triazoles, [8] likely due to the ring-chain tautomerism of the latter. [9] Among the reactive triazoles are 1-sulfonylated derivatives which can be synthesized in multigram amounts, isolated, and safely stored, [8e] or can be generated in situ from stable N H -triazoles, 1 , with triflic anhydride under mild conditions (Scheme 1). [6d] In the presence of Rh(II) catalysts, N -triflyl triazoles formed in this way are readily converted to azavinyl carbenes that readily react with a variety of olefins, 2 , yielding highly enantioenriched cyclopropane carboxaldehydes, 3 .…”