On the selenepin/benzene selenide valence tautomerizations: electronic and steric effects at theoretical levels

Abstract

Tautomerization in selenepin (1) benzene selenide (2) binary system is found to favor, 2, at HF, MP2, and B3LYP levels, using 6-311G* basis set. Electronic effects appear to have small effects on 1 2 equilibria and show little impact on the conformational ring inversions of 1, at the same levels. In contrast, steric effects effectively decrease DH values in an order inversely proportional to the size of the substituents employed (Me [ Et [ i-Pr). A possible Se extrusion is suggested to be the main reason why no 2 has ever been detected experimentally.

Synthesis of π-conjugated polycyclic compounds by late-stage extrusion of chalcogen fragments

“…In contrast with the parent oxepine, which is isolable at room temperature, other group-16 heteropines suffer from thermal instability. Indeed, the low activation barrier for S, Se or Te cheletropic extrusion from the norcaradiene valence isomer, combined with the irreversibility of this process, shifts the tautomerization equilibrium and delivers benzene as the organic product along with inorganic species [41][42][43][44]. Over the years, many efforts were thus devoted to the synthesis of thiepine derivatives with increased thermal stability, with the aim to disfavor the formation of the transient thianorcaradiene intermediate as a way to prevent the sulfur extrusion [44].…”

Effects of fused benzene rings on tautomerizations and inversions of benzo, azabenzo, and oxabenzocycloheptatrienes at theoretical levels

“…The thermal rearrangement of puberulin to isopuberulin takes place through an intermediate with a core of 6H-benzocycloheptatriene (3B CH 2 ) (Scheme 1) [10]. This kind of rearrangement, along with our previous studies on heteropines [11][12][13][14][15], and the scarce documents on thermal rearrangements of benzocycloheptatrienes, stimulated us in taking up the valence tautomerizations and inversions of nB CH 2 (n = 1-3) (Scheme 2).…”