Oxidative ring expansion of 3-hydroxy-3-phenacyloxindoles using phenyliodine diacetate and molecular iodine: Synthesis of 2-hydroxy-2- aryl/alkyl-2,3-dihydroquinolin-4(1H)-ones Ashish C. Kavale, Amit H. Kalbandhe, Imran A. Opai, Atul A. Jichkar, Nandkishor N. Karade Department of Chemistry, Rashtrasant Tukadoji Maharaj Nagpur University, Nagpur, Maharashtra 440 033, India article info Article history: Received 21 September 2020 Revised 1 November 2020 Accepted 4 November 2020 Available online xxxx Keywords: Aldol reaction Isatin Tertiary alcohol oxidation Rearrangement Quinolone derivatives Isocyanate abstract Oxidation of tertiary alcohol of the type 3-hydroxy-3-phenacyloxindoles using the combination of phe- nyliodine diacetate and molecular iodine in methanol results in oxidative cleavage of C2-C3 bond to form isocyanate as an intermediate with its subsequent trapping by methanol to form ortho-carbamates of 1,3- diaryl carbonyl compounds which further undergoes concurrent cyclization to furnish 2-hydroxy-2-aryl/ alkyl-2,3-dihydroquinolin-4(1H)-ones derivatives in good yields. Ó 2020 Elsevier Ltd. All rights reserved. 2-Arylquinolin-4(1H)-ones are privileged heterocyclic scaffolds and found as structural sub-units of many biologically active natu- ral products [1] and pharmaceuticals exhibiting antidiabetic [2], antiviral [3], antimitotic [4], antimalarial [5], and HIV-1 integrase inhibitory properties [6]. Moreover, quinolin-4(1H)-one can serve as a synthetic intermediate as it permits structural modifications at 1, 3 and 4-positions resulting in the synthesis of ‘‘drug like” molecule with diverse biological profile [7]. Owing to these wide range of biological properties, numerous methods have been developed for efficient synthesis of 2- arylquinolin-4(1H)-one derivatives. The most common methods (Scheme 1) available for the synthesis of 2-arylquinolin-4(1H)- one involve (i) base-promoted cyclization of N-(o-ketoaryl) amides, known as the Camps cyclization [8] (ii) transition metal catalyzed cyclizations of o-haloarylacetylenic ketones/amines or o-alkynyl- benzamides/aldehydes [9] (iii) TEMPO-promoted intra-molecular oxidative Mannich reaction from N-arylmethyl-2-aminophenyl ketones [10] (iv) reductive cyclization of 2-nitrochalcones pro- moted by TiCl 4 /Zn [11] (v) base induced cyclization of a-alkyl N-aryl- a -aminonitriles [12] (vi) palladium-catalyzed intramolec- ular N-arylation of in situ generated enamine from the reaction of (Z)-b-chlorovinyl ketone with amine [13] and (vii) copper- catalyzed heterocyclization of 1-(2-bromophenyl)- and 1-(2-chlorophenyl)-2-en-3-amin-1-ones [14]. The applications of hypervalent iodine mediated Hofmann rearrangement is also demonstrated for the metal-free synthesis of 4-quinolones deriva- tives from 2-alkynylbenzamides [15]. However, some of these reported methods of 2-arylquinolin-4(1H)-one synthesis are gen- erally associated with requirement of special starting materials, multistep procedures and narrow substrate scope. Hypervalent iodine compounds [16] have emerged as highly versatile reagents for the oxidation of alcohols [17] due to its com- mercial availability, mild reaction conditions, environmentally benign attributes, high functional group tolerance and similar reac- tivities to those of toxic heavy metal-based oxidants. For example, the cyclic tertiary allylic alcohols undergo oxidative rearrangement to form b-disubstituted a, b -unsaturated ketones or aldehydes using pentavalent iodine reagent such as IBX in DMSO [18]. Earlier to this report, toxic oxochromium(VI)-based (Collins reagent, PCC and PDC) reagents were employed for the oxidation of cyclic ter- tiary allylic alcohols [19]. Several improvements were then reported for the oxidation of tertiary allylic alcohol using other oxi- dants such as Re 2 O 7 or Bi(OTf) 3 /TEMPO/PhIO [20], 2-iodoxyben- zenesulfonic acid/oxone [21] and TEMPO-derived oxoammonium salts [22]. The oxidative rearrangement of other variety of tertiary benzylic alcohols attached at para-position of phenols is also doc- umented using phenyliodine diacetate (PIDA) as metal-free oxi- dant [23]. https://doi.org/10.1016/j.tetlet.2020.152631 0040-4039/Ó 2020 Elsevier Ltd. All rights reserved. Tetrahedron Letters xxx (xxxx) xxx Contents lists available at ScienceDirect Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet Please cite this article as: A.C. Kavale, A.H. Kalbandhe, I.A. Opai et al., Oxidative ring expansion of 3-hydroxy-3-phenacyloxindoles using phenyliodine diac- etate and molecular iodine: Synthesis of 2-hydroxy-2-aryl/alkyl-2,3-dihydroquinolin-4(1H)-ones, Tetrahedron Letters, https://doi.org/10.1016/j. tetlet.2020.152631