Introduction
In recent times, several advancements were made in using catalytic amounts of iodine
in combination with tert-butyl hydroperoxide (TBHP) as co-oxidant. The increased utility is mainly due to
its inexpensive, environmentally benign nature, good efficiency and compatibility
to work in place of rare or toxic heavy metal oxidants.[1] The I2/TBHP catalytic system works efficiently for numerous C–C and C–X (X = heteroatom)
bond-forming organic transformations under mild reaction conditions to offer the desired
products in excellent yields.[2]
Table 1 Use of Iodine–TBHP
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(A) Jiang et al. reported an I2/TBHP mediated domino oxidative cyclization for the one-pot synthesis of polysubstituted
oxazoles from readily available styrenes and benzylamines under mild conditions.[3]
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(B) Zhang et al. demonstrated the synthesis of 2-phenylquinazolines in good to excellent
yields via tandem sp3 C–H functionalization of 2-amino benzophenones and benzylic amines.[4]
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(C) Manjunath and Prabhu reported a metal-free catalytic route to 2-aminobenzoxazoles
by amination of benzoxazoles via C–H bond activation of primary or secondary amines.
Further the methodology was demonstrated to synthesize therapeutically active benzoxazoles.[5]
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(D) An I2/TBHP catalyzed first efficient and direct synthesis of tertiary amides from alcohols
and dimethylformamide has been developed. This transition-metal-free protocol provides
a practical synthetic tool for the construction of N,N-dimethyl-substituted amides.[6]
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(E) A metal-free oxidative coupling of methyl ketones and primary or secondary amines
to α-keto amides was developed by Wan and his group. Four types of intermediates,
α-iodo ketones, α-amino ketones, iminium intermediates and α-hydroxy amines were identified
through a series of control experiments. The atom-economic methodology can be scaled-up,
tolerates a variety of functional groups, and is operationally simple.[7]
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(F) A novel I2/TBHP catalyzed selective 2-arylsulfonylation of indoles was demonstrated. Various
substituted 2-arylsulfonyl indoles were obtained in good to excellent yields in one
pot. The direct sulfonylation reaction occurred selectively at C-2 position of the
indole ring and only a catalytic amount of iodine acted as an efficient promoter.
This method is a novel alternative approach for the synthesis of biologically important
hetero diaryl sulfones from sodium sulfinates.[8]
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(G) Recently, we have developed an I2/TBHP mediated synthesis of isatin and iodoisatin from 2′-aminoacetophenone via intramoleular
oxidative amidation of the sp3 C−H bond. The reaction proceeds through sequential iodination, Kornblum oxidation,
and amidation in one pot. The stoichiometric amount of I2 plays a significant role in delivering iodoisatin exclusively in high yields.[9]
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(H) Ji’s research group reported an I2/TBHP mediated oxidation of commercially available indoles to isatins in moderate
to good yields.[10]
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