Cyclic selenonium exo-ylides (3,4-dihydro-1H-2-benzoselenin-2-io)methanides; syntheses and reactions

Abstract

Reactions of the title compounds (III) are investigated giving the products shown in the scheme.

Synthesis and Orthogonal Functionalization of [60]Fullerene e,e,e‐Trisadducts with Two Spherically Defined Addend Zones

“…Depending on the reaction conditions, the benzylic ethers of 14 were cleaved to yield alcohol or bromide derivatives (Scheme 3). Heating a two-phase system of CHCl 3 and 48 % HBr in water with 14 and the phase-transfer catalyst CTAB [55] to reflux for seven days gave tribromide 33 in reasonable yield. Furthermore, treating a solution of 14 in CH 2 Cl 2 with boron trichloride and subsequent aqueous workup led to the formation of triol 34 in good yield (Scheme 3).…”

Selenonium Ylides: Syntheses, Structural Aspects, and Synthetic Applications

“…Thus, the diastereoisomeric purity of the diastereoisomeric mixture of ylide 15 was determined from the integration of their 1 H-NMR signals at the ortho-position of the aromatic ring or at the MeSe signal using the shift reagent [32]. The analysis of the 1 H-NMR spectra of the cyclic exo-ylides, (3,4-dihydro-1H-2-benzoselenin-2-io)methanides 18a-e (Figure 12), which showed AB quartets assigned to 1-H of the methanide entities occupying the sterically relaxed pseudo-equatorial positions, allowed the suggestion of the preference for the given conformation of the 6-membered saturated selenocyclohexane, as the protons cis to the 1-and 4-positions of the methanide groups appear at lower magnetic fields as a result of the anisotropic effects of the methanide entities [37].…”

“…The lack of broadening of the methyl peak in the 1 H-NMR spectrum of the selenonium ylide 11 upon cooling to −60 °C indicates that the equilibration of the two methyl groups proceeds via an energy barrier of <10 kcal/mol [28]. This value is lower than that of the sulfonium ylide Me2SC(COCMe)2 for which a barrier of 12 kcal/mol (based on C-methyl signals broadening at −25 °C) was reported [37]. The 1 H-NMR spectra were used for the determination of the diastereoisomeric excesses of selenonium ylides 15a and 15b.…”

“…100 cm −1 to a lower frequency than the typical absorption for the carbonyl and cyano groups. These shifts were explained by assuming that the ylidic carbanions are delocalized over the electron-withdrawing carbonyl and/or cyano groups [37]. From time to time, UV-VIS data is attached to the spectroscopic characteristics of a given selenonium ylide.…”

“…This method was successfully applied in the synthesis of stable cyclic selenonium exo-ylides 18, which were obtained in a two-step process from 3,4-dihydro-1H-2-benzoselenin (63) (Scheme 18) [37]. In the first step, selenide 63 was reacted with chloramine T trihydrate to give N-p-tolueneselenimide 64, which in the next step was treated with five equivalents of activated methylene compounds, such as acetylacetone, methyl acetoacetate, dimethyl malonate, methyl cyanoacetate, and malononitrile, to give selenonium ylides 18a-e, respectively.…”