Oxidative Cationic Cyclizations, Rearrangements and Fragmentations

Hypervalent iodine(III) compounds, such as [bis(trifluoroacetoxy)iodo]benzene, (diacetoxyiodo)benzene and [hydroxy(tosyloxy)iodo]benzene, are commonly used as reagents in various cationic cyclizations, rearrangements and fragmentations. Numerous examples of such reactions have been reported in the literature and summarized in the reviews dedicated to synthetic applications of hypervalent iodine compounds [4,7,10,11, 180, 191, 387]. 

This methodology with some variations has been utilized in the synthesis of numerous heterocyclic systems, such as heterocycle-fused quinolinone derivatives [391], l,4-benzodiazepin-2-ones [392], benzo-, naphtho- and heterocycle-fused pyrrolo[2,l-c][l,4]diazepines [393], quinolinone or pyrrolidinone derivatives [394], dibenzo[fl,c]phenanthridines [395], thiazolo-fused quinolinones [396], isoindolinone and isoquinolin-2-one derivatives [397], indoline derivatives [398], 5-aroyl-pyrrolidinones [399,400], indazolone derivatives [401,402], substituted indolizidinones [403], 1-arylpyrrolopyrazinones [404], stmcturally diverse 

R = Ph, 2-MeC6H4,4-MeOC6H4,4-CIC6H4, 2-thienyl, PhCH=CH, etc. Ar = 4-MeOCeH4 

Additional examples of synthetic applications of hypervalent iodine-induced heterocyclizations include the following the metal-free one-pot synthesis of 2-acylbenzothiazoles by oxidative cyclization of multiform substrates [434], iodine(III)-mediated tandem oxidative cyclization for construction of 2-nitrobenzo[ ]furans [435], hypervalent iodine mediated oxidative cyclization of o-hydroxystilbenes into benzo- and naphthofu-rans [436], PhI(OCOCF3)2-mediated synthesis of 3-hydroxy-2-oxindoles and spirooxindoles from anilides [437], synthesis of isoxazoles by hypervalent iodine-induced cycloaddition of nitrile oxides to alkynes [438], 

A synthetically useful oxidative fragmentation of tertiary cyclopropyl alcohols (e.g., 356) with [bis(trifluoroacetoxy)iodo]benzene, which produces alkenoic acids or esters, has been reported [459,460]. 

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