α-Angelica lactone catalyzed oxidation of benzylic sp³ C–H bonds of isochromans and phthalans

Abstract

Oxidation of benzylic sp3 C–H bonds of isochromans and phthalans to isocoumarins and phthalides has been achieved by employing α-angelica lactone as an organocatalyst.

Iron nitrate and 4-OH-TEMPO-cocatalyzed aerobic oxidation of isochromans

“…In addition to isochromans, the reaction of xanthene 4 could be performed well under the standard conditions, giving xanthone 5 in 100% yield (eqn (1)). With 2 mol% each of Fe(NO 3 ) 3 ·9H 2 O and 4-OH-TEMPO in MeCN, phthalan 1q was successfully transformed into phthalide 2q in 60% yield, 3 a ,4 b,c,f,n – p ,6 a , e ,7,8 l–n ,10 a–c , e , h , i , m , n ,11 c ,13 although 12% yield of o -phthalaldehyde 3q was observed (eqn (2)). In addition, the practicality has been demonstrated by applying 10 mmol of 1a , affording 1.4506 g of 2a in 98% yield (eqn (3)).…”

“…12 The presence of peroxide intermediates cannot be excluded: radical 1a′ could react with O 2 to afford peroxyl radical species Int 4 , which could be further transformed to afford lactone 2a . 6 b ,7…”

“…2 Direct aerobic oxidation of isochromans was reported; however, a high temperature of 80 or 140 °C was required (Scheme 1a). 3 Recently, photoredox catalysts, 4 electrochemical catalysts, 5 acid catalysts, 6 organocatalysts, 7 nitroxyl catalysts, 8 doped carbon materials, 9 and transition metal catalysts 10 have been employed in the aerobic oxidation of isochromans. Iron-based catalysis has received much attention because of its natural abundance, low cost and environmentally friendly nature (Scheme 1b): 11 Xiao and coworkers reported Fe(OTf) 2 with a PyBisulidine ligand with low conversion with 1,1′-oxidi-isochromans as the byproducts; 11 a in 2017, Shen et al .…”

Efficiently Aerobic Dehydrogenation of N‐Heterocycles and Hydrocarbons over MnAl Oxides

“…[3,34] Additionally, when a control experiment was conducted in the presence of 1 equiv. of CuCl 2 (Scheme 3C), which is always used as an electron remover, [34,35] the yield of 2 a was significantly decreased, indicating that the MnAlO-catalyzed aerobic dehydrogenation proceeded mainly through an electron transfer mechanism.…”