C-H iodination

More recendy, the same group came up with an N-arylcarboxamide-directed Pd-catalyzed ortho- C—H iodination of (hetero)arenes (58 59)... 

Scheme 21 Pd-catalyzed regioselective C—H iodination of heterocycles directed by a carboxamide group featuring a 4-trifluoromethyl-2,3,5,6-fluorophenyl substituent.

Furthermore, both C-H iodinations and brominations can be achieved using the respective hahde salts in combination with oxidants [148]. Scheme 23.46 shows one example of this approach, in which calcium halides act as halide sources for C-H bond halogenations with Cu(02CCF3)j as stoichiometric oxidant [142]. 

C-H methyl C-H, iodine (CH3I) C-H methyl, CH3I Halogenated (CH3I)... 

The stiochiometry of the reaction was measured by reacting Pu metal with a THF solution of C2Rll2 in a sealed, evacuated flank. After 24 hours, volume and pressure measurements showed that 1.46 mm of gas was evolved, after correction for the vapor pressure of THF 1.54 mm of Pu was consumed, and titration of the THF filtrate found 1.8 mm of iodine. The gas composition was not determined, but assuming that the evolved gas was C H, these data indicate that the reaction is ... 

In oleum, the kinetic isotope effect, indicating that C—H bond-breaking is involved in the rate-limiting step of the reaction, i.e. that k j > 3. 

Another approach for the chemoselective and asymmetric iodination of unactivated C H bonds was reported with a palladium catalyst using a chiral auxiliary (Scheme 5.19). Excellent diastereoselectivities were induced by chelating the auxiliary to the palladium catalyst center followed by an electrophilic C—H activation and iodination. Studies showed that I2 acts as both the reactant and the activator to form the reactive catalyst precursor, Pd3(OAc)3. After the reaction was completed, the formed Pdl2 was precipitated from the solution and could be reused several times without losing reactivity and selectivity. 

Oxidative C-H amination has been an area of intensive research since the publication of CHEC-II(1996). This methodology has been applied to the synthesis of a variety of 1,2-thiazine 1,1-dioxides. In the simple cases, substrates containing an aromatic C-H can be cyclized in the presence of hypervalent iodine. For instance, the reaction of A-methoxy(2-arylethane)sulfonamide 202 with [hydroxyl(tosyloxy)iodo]benzene rapidly affords benzenesulfon-amide 203 in excellent yield (Equation 30) <20030BC1342> see also <2000JOC926> and <2000JOC8391>. 

The C-H insertion of alkyl sulfonamides using hypervalent iodine reagents in the presence of a transition metal catalyst was initially disclosed by Dauban and Dodd <20000L2327>. In this report, sulfonamide 204 was treated with PhI(OAc)2 and base to form an intermediate iminoiodinane 205 (Scheme 28). The material 205 was first... 

In spite of its formal similarity to the above mentioned annulation processes, the reaction shown in 4.37. includes a unique migration step. Oxidative insertion of the palladium into the phenyl-iodine bond is followed by the migration of the palladium onto the more electron rich indole ring. The 2-indolylpalladium complex than carbopalladates the pendant alkync moiety and the process ends by the formal activation of a C-H bond of the phenyl substituent and subsequent reductive elimination, furnishing the pentacyclic product.48 The same strategy has been utilised in the preparation of the indoloindolone framework from /V-bcnzoyl-3-(o-iodophcnyl)-indolc in an oxidative addition - palladium migration - C-H activation sequence.49... 

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