Ipso-arylation

The synthesis of the tellurophene-containing low-bandgap polymer PDPPTe2T by microwave-assisted, palladium-catalyzed, ipso-arylative polymerization of 2,5-bis[(a,a-diphenyl)methyl]tellurophene in the presence of diketopyrrolopyrrole (DPP) monomer was reported (14AG(1)10691). This is the first PV device prepared from a tellurophene polymer. IPCE measurements showed that substitution from sulfur to tellurium causes a red shift in absorption and enables donor materials to collect up to 1 pm. 

As described above regarding the behavior of aromatic carboxyhc acids, tert-benzyl alcohols are also unique substrates, which undergo not only hydroxy-directed ortho-arylation via C—H bond cleavage, but also ipso-arylation via C—C bond cleavage involving P-carbon elimination with the hberation of a ketone molecule (Scheme 4.84) [88]. 

The preparation of aromatic fluorine compounds may be accomplished by direct fluorination or by fluonnation of organometallic intermediates. Tlte ipso fluorination of an aryl organometallic derivative with a positive fluorine reagent allows control over the regioselectivity of the fluorination and offers advantages in the preparation of F-labeled materials [II, 50],... 

In contrast to 2,3-dioxygenases, the related ipso/ortho oxygenation of aryl carbox-ylates has received considerable less attention and has hardly been utilized by the synthetic community, so far. Biooxidation of benzoic acid and P-naphthalene carboxylate provide access to corresponding 1,2-dihydroxylated dihydroaryl compounds in excellent stereoselectivity (Scheme 9.35), analogous to TDO- and NDO-mediated ortho/meta oxygenations. Whole-cell-mediated biotransformations were performed with mutant strains of Rahtonia and Pseudomonas and enable access to preparative quantities in >5 gl titers [261,262]. 

An example of this displacement between a pyridine nitrogen atom and an aryl halide is shown in Scheme 21. When 2-pyridyl acetates 138 were C-acylated with 2-halobenzoyl chlorides, the enolized products 139 resulting from the reaction suffered an intramolecular nucleophilic attack of the pyridine nitrogen atom onto the ipso-position to give benzo[c]quinolizinium salts 140 as intermediates. Loss of HC1 gas from 140 afforded benzo[c]quinolizine derivatives 141 <2002JOC2082>. 

Incorporation of additional donor functionality into the periphery of phosphinomethanide ligands also has dramatic consequences for the structures of their alkali metal complexes. The complex [Li C(SiMe2Ph)(PMe2)2 ]3 (49) crystallizes as solvent-free cyclic tri-mers (Fig. 18), in which each lithium is primarily coordinated by two P atoms from one ligand and the carbanion center of an adjacent ligand (138, 139). This is supplemented by an essentially -interaction with the ipso and an ortho-carbon of the phenyl ring associated with the carbanion bonded to lithium. Each Li is thus bound by two P atoms, two aryl carbons, and a central carbon of the phosphinomethanide ligands. 

Recently, Curran described a procedure using triethylborane for the synthesis of spirooxindoles and spirodihydroquinolones through intramolecular addition of aryl radicals at the ipso position 4-alkoxy-substituted aromatic rings [15]. The key step for a formal synthesis of the vasopressin inhibitor SR121463A is described in Scheme 5. The initiation was performed with Et3B in an open to air reaction vessel. 

In these reaetions, the most reliable mechanism is considered to involve the initial metal-coordination at the nitrogen atom of the pyridine ring and the subsequent attack of an alkyl or aryl anion at the most probable cationic sites on the ring, namely, the 2- and/or 4-position of the ring. If a 2-halogen substituted pyridine is used, the nucleophilic anion attacks the 6-position. Thus, the addition is a more prefered reaction than the ipso-substitution as shown in reaction (29). The substitution of amide or phenyl-... 

Under the influence of a Lewis acid, Cjq can be arylated via a Eriedel-Crafts reaction (see Section 8.6). A similar reaction occurs with CggEjg where ipso substitution of fluorine atoms takes place [68]. The fluorofullerene is treated with FeClj in benzene for two weeks (Scheme 9.8). Electrophilic substitution leads to arylated C5QFjg Ph with n = 1-3. Probably due to steric reasons the 5-substitution is not observed in this arylation. 

---