Iodine-catalyzed intramolecular oxidative

An iodine-catalyzed intramolecular oxidative thiolation of vinylic carbon-hydrogen bonds via tandem iodocyclization and dehydroiodination has also been developed for the construction of 2-methylene-3-thiophe-nones (14ASC743).The synthetic strategy was extended to the preparation of 2-methylene-3-benzothiophenone via the cyclization of o-methylthio-phenyl vinyl ketones. 

Hypervalent iodine(III) mediated/catalyzed intramolecular oxidative C-H bond functionalization of (hetero)arenes and alkenes has been widely applied in the synthesis of several biologically active heterocyclic scaffolds. This intramolecular oxidative C-H bond functionalization reaction leads to the formation of carbon-carbon and carbon-heteroatom bonds in an efficient manner. Of all bond formation reactions, C-N bond annulations have been exploited most and are of immense... 

In this reaction, initially, acetophenone 36 was converted to a-iodo acetophenone 39 by iodine, which was further transformed into phenyl glyoxal 40 by DMSO (dimethyl sulfoxide). The formed aldehyde then reacted with 2-aminothiophenol 37 to provide intermediate 41, which was further converted to 42 through an intramolecular 1,2-addition. Then, 42 underwent iodine-catalyzed oxidative dehydrogenation to afford the desired product 2-acyl benzothiazole 38 (Scheme 9.9). Very recently, the same authors reported the synthesis of 2,5-disubstituted oxazoles using a similar domino process [17]. 

Baylis-Hillman adducts such as 55 and 56 derived from 2-nitrobenzaldehydes were shown to function as useful precursors to functionalized (1H)-quinol-2-ones and quinolines. Treatment of 55 and 56 with iron and acetic acid at 110 °C afforded 57 and 58, respectively <02T3693>. A variety of other cyclization reactions utilized in the preparation of the quinoline scaffold were also reported. An iridium-catalyzed oxidative cyclization of 3-(2-aminophenyl)propanols afforded 1,2,3,4-tetrahydroquinolines <02OL2691>. The intramolecular cyclization of aryl radicals to prepare pyrrolo[3,2-c]quinolines was studied <02T1453>. Additionally, photocyclization reactions of /rans-o-aminocinnamoyl derivatives were reported to provide 2-quinolones and quinolines <02JHC61>. Enolizable quinone and mono- and diimide intermediates were shown to provide quinolines via a thermal 6jt-electrocyclization <02OL4265>. Quinoline derivatives were also prepared from nitrogen-tethered 2-methoxyphenols. The corresponding 2-methoxyphenols were subjected to a iodine(III)-mediated acetoxylation which was followed by an intramolecular Michael addition to afford the quinoline OAc O... 

While the majority of Rh-catalyzed C-H amination processes employ hyperva-lent iodine oxidants and sulfonamide derivatives, Lebel and coworkers have demonstrated that /V-tosyloxycarbamates will engage with catalytic Rh2(02CCPh3)4 and K2CC>3 to afford products of intramolecular C-H insertion (Fig. 22) [104, 5, 105]. Similar to Du Bois earlier work involving oxidative cyclization with 1 ° carbamates [94], the /V-tosyloxy derivatives display a strong bias for oxazolidinone formation. Selectivity trends and other mechanistic data support a reaction pathway involving a Rh-nitrene oxidant. Intermolecular amination of simple benzylic substrates... 

Several examples of cyclizations through intramolecular C-N bond formation catalyzed by hypervalent iodine species have been reported. Antonchick and coworkers developed an efficient organocatalytic method for the preparation of carbazoles through catalytic oxidative C-N bond formation [48]. The best yields of products were obtained in hexafluoro-2-propanol using 2,2 -diiodo-4,4, 6,6 -tetramethylbiphenyl (42) as the catalyst and peracetic acid as the oxidant, as illustrated by a representative example shown in Scheme 4.23. 

As described in Sect. 2.1.2, the a-functi(Mialization (tosylation, triflation) of ketones with hypervalent iodine, followed by nucleophilic attack by diverse nucleophiles in an intramolecular fashion offers a convenient entry to various heterocycles [6]. Such a transformation can also be realized in an intermolecular fashion. Along these lines, Togo and coworkers [97] reported an elegant one-pot synthesis of 2,4,5-trisubstituted oxazoles 142 from alkyl aryl ketones 140 and nitriles 141 via an iodoarene-catalyzed oxidation reaction (Scheme 35). In this reaction sequence, reactive aryliodonium species were generated in situ by the reaction of aryl iodide with mCPBA and trifluoromethanesulfonic acid (TfOH). Afterwards, aryliodOTiium species reacted with alkyl aryl ketone to form a fi-keto aryliodonium species. 

The rhodium(II)-catalyzed intermolecular C(sp )—H amination reaction involves the use of the more soluble hypervalent iodine oxidant PhI(OCOiBu)2 which enables its slow addition over several hours, a protocol that increases the yield of the nitrene insertion. But contrary to the intramolecular process, it does not require the presence of magnesium oxide, a point that puts into question its presumed role of acid scavenger." It should be mentioned that these conditions have also proved appropriate to perform the... 

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