Recent advances in the transition metal-free oxidative dehydrogenative aromatization of cyclohexanones

Abstract

Cyclohexanones are simple and widely available raw materials that could be obtained from lignin biomass, highlighting their renewable and sustainable features. Cyclohexanones, as an important synthon in organic chemistry, have...

KI-mediated three-component annelation for the regioselective synthesis of angular azolo[1,5-a]pyrimidine derivatives

“…The use of I 2 , NH 4 I, or NaI resulted in lower yields (Table 1 entries 8-10). Other solvents, such as toluene, 1,4-dioxane, NMP, DMF, and acetonitrile, were not suitable for the reaction, leading to lower yields for 4a (Table 1 entries [11][12][13][14][15]. Notably, the corresponding cyclic product (4a) was furnished in the same yields at 120 1C (Table 1 entry 16).…”

“…To the best of our knowledge, this is the first example of a KI-mediated three-component reaction for the preparation of angular 6,7,8,9-tetrahydropyrazolo[1,5- a ]quinazolines in a neutral system (Scheme 1c). It is worth mentioning that this protocol exhibits a high regioselectivity to produce an angular skeleton instead of a linear one 10 and blocks over-aromatization processes 11 even in an oxidative system.…”

Reductive thiolation and oxidative dehydroaromatization of cyclohexanones with primary amines and sodium sulfinates to access o-sulfanylanilines

“…Recently, cyclohexanone as a viable aryl precursor has attracted enormous attention from the synthetic community. 1 The dehydrogenative functionalization of cyclohexanone provides a new platform to access polyfunctional aromatic compounds via various transformations. 2 This strategy not only provides a good complement to existing metal-catalyzed cross-coupling and electrophilic/nucleophilic substitution reactions of aromatic compounds but also overrides the inherent limitations of frequently used arylation reagents.…”

An I2–DMSO catalytic manifold enabled aromatization for C-ring editing of podophyllotoxone

“…Notwithstanding the progress recorded by different synthetic tactics such as metal-catalytic, 10 sulfur-promoted, 11 electrocatalytic, 12 a photocatalytic 12 b , c and other metal-free 13 oxidations to realize the dehydrogenative aromatization of cyclohexanones giving access to phenols or aromatic amines, the aromatization of the C-ring of podophyllotoxone remains an independent and challenging scenario, due to its special structural characteristics. Indeed, the sterically inhibited 2-substituted α-tetralone skeleton has been reported to be unreactive in some palladium-catalyzed aromatization, 10 c and the electron-donating E-ring residue and its electrophilic benzyl site are also risky for single-electron oxidation.…”