Spirofused and Annulated 1,2,4‐Trioxepane‐, 1,2,4‐Trioxocane‐, and 1,2,4‐Trioxonane‐Cyclohexadienones: Cyclic Peroxides with Unusual Ring Conformation Dynamics

Abstract

C3- or C4-hydroxyalkylated phenols are highly reactive towards peroxidation with oxone, which results in the formation of tertiary C3 hydroperoxides. This reaction can also be performed with photochemically generated singlet oxygen. However, other characteristic singlet oxygen reactions do not proceed with caroate. The initially formed hydroperoxides cyclize in the presence of a Lewis acid catalyst based on boron, indium, or iron to give spiroannulated peroxides. These exhibit restricted ring inversion whereas larger nine-membered-ring peroxides are thermally less stable and show higher ring flexibility (according to NMR analysis).

Atom Economical Photocatalytic Oxidation of Phenols and Site-Selective Epoxidation Toward Epoxyquinols

“…Yield: 91%; yellowish solid; mp 91–93 °C; 1 H NMR (400 MHz, CD 3 OD) δ 6.94 (d, J = 8.1 Hz, 1H), 6.83 (d, J = 2.7 Hz, 1H), 6.58 (dd, J = 8.1, 2.7 Hz, 1H), 4.54 (s, 2H), 2.20 (s, 3H); 13 C­{ 1 H} NMR (100 MHz, CD 3 OD) δ 156.4, 141.4, 131.9, 127.5, 115.5, 114.9, 63.3, 17.7; IR (ATR, cm –1 ) 3335 (OH); HRMS (ASAP–/TOF) calculated for C 8 H 9 O 2 [M – H] − 137.0603, found 137.0604. Spectral data are in accordance with existing literature …”

Multigram Synthesis of Trioxanes Enabled by a Supercritical CO2 Integrated Flow Process

“…18,19 Moreover, para-peroxyquinols are valuable as intermediates for the preparation of a diverse range of synthetic scaffolds. 20 Griesbeck and co-workers 21 have an outstanding record in developing methodologies to access new trioxanes including the use of both chemically and photochemically generated singlet oxygen, 1 O 2 , to access spirofused and annulated cyclic peroxides of varying ring sizes so as to examine their conformational and thermal stability. More generally, the synthesis of 1,2,4-trioxanes has been achieved by the dearomatization of phenol using 1 O 2 , which can be generated either photochemically 21 or chemically 22 (e.g., from commercially available oxone, (KHSO 5 )).…”

“…20 Griesbeck and co-workers 21 have an outstanding record in developing methodologies to access new trioxanes including the use of both chemically and photochemically generated singlet oxygen, 1 O 2 , to access spirofused and annulated cyclic peroxides of varying ring sizes so as to examine their conformational and thermal stability. More generally, the synthesis of 1,2,4-trioxanes has been achieved by the dearomatization of phenol using 1 O 2 , which can be generated either photochemically 21 or chemically 22 (e.g., from commercially available oxone, (KHSO 5 )). Therefore, the use of 1 O 2 on scale would open up very economical routes to high-value compounds, but unfortunately, all of this work involved batch reactions, which are hard to scale-up both on safety grounds (e.g., larger inventories of hazardous intermediates) and the more generic problems of scaling-up photochemical reactions.…”

Spiroverknüpfte und ringanellierte 1,2,4‐Trioxepan‐, 1,2,4‐Trioxocan‐ und 1,2,4‐Trioxonan‐Cyclohexadienone: cyclische Peroxide mit ungewöhnlicher Ringkonformationsdynamik

“…[22] Abbildung 1. Wirw aren zunächst von der Komplexitätd er NMR-Spektren dieser Verbindungen überrascht:I nd en 1 H-NMR-Spektren erschienen alle vinylischen Cyclohexadienon-Wasserstoffatome bei unterschiedlichen chemischen Verschiebungen, ebenso die formal enantiotopen Methylgruppen bei d = 1.3 und 1.6 ppm (Abbildung 1).…”

“…[17] Diese Annahme erscheint plausibel, da Singulett-Sauerstoff ( 1 O 2 )b ereits als Zersetzungsprodukt von Caroscher Säure sowohl unkatalysiert als auch Keton-katalysiert nachgewiesen wurde. [20] [22] Abbildung 1. 1 H-NMR-Spektren von 6a (oben) und 6b (unten) in CD 3 OD.…”