Diastereoselective Aerial Oxidative Cyclization of Methylenebisnaphthols Catalyzed by N-Hydroxyimides in the Presence of Fe³⁺ and Co²⁺-Mn²⁺ Catalysts

Abstract

Aerial oxidative cyclization of methylenebisnaphthols to their corresponding spirans has been carried out using catalytic amounts of N-hydroxyimides and FeCl3·6H2O or Co(OAc)2·4H2OMn( OAc)2·4H2O. In this article we focus on the use of FeCl3·6H2O as a highly green and sustainable catalyst.

Aerobic Copper Catalytic Oxidation of Methylene and Arylidenebisnaphthols: A Green and Efficient Synthesis of Spironaphthalenones

“…Two diastereoisomeric spiroketones X and Y are likely to be formed during the course of the reaction (Figure ). According to the operating conditions, especially in catalytic conditions, a mixture of the diastereoisomer X and the diastereoisomer Y was usually obtained …”

“…Depending on the conditions, the reaction proved to be stereoselective,,, or lead to a mixture of diastereoisomers ,,. Moreover, the reaction conditions are very often stoichiometric and only more recently catalytic conditions were reported.…”

“…Depending on the conditions, the reaction proved to be stereoselective [9,10,13,16] or lead to a mixture of diastereoisomers. [12,14,15] Moreover, the reaction conditions are very often stoichiometric and only more recently catalytic conditions were reported. Iron salts have been proposed as catalyst in the presence of a re-oxidant: iron carboxylate with hydrogen peroxide [13] or TEMPO, [14] N-hydroxyimides [15] and oxygen.…”

“…[12,14,15] Moreover, the reaction conditions are very often stoichiometric and only more recently catalytic conditions were reported. Iron salts have been proposed as catalyst in the presence of a re-oxidant: iron carboxylate with hydrogen peroxide [13] or TEMPO, [14] N-hydroxyimides [15] and oxygen. However, in these most attractive reaction conditions, i. e. catalytic, the reactions are generally non-stereoselective.…”

“…However, in these most attractive reaction conditions, i. e. catalytic, the reactions are generally non-stereoselective. [13][14][15] An exception was the use of triphenylbismuth [16] as catalyst, which was found efficient in stereoselectivity. We have decided to try to reproduce the catalytic oxidation of 4,4'-(phenylmethylene)bis(naphthalen-2-ol) 2 f by triphenylbismuth according to the description of Khoramadi-zad et al [16] Surprisingly, we did not obtain any oxidation product but only the dehydration product of 2 f: the 14-(phenyl)-14H-dibenzo[a,j] xanthene [17] (see experimental part).…”