Iodide- arylating reagents

Aryl iodides. Aryl iodides can be prepared by reaction of arenes with I2 and a mixture of A1C13 and CuCI 2. Yields are moderate to good, but the reaction fails with ethyl benzoate, acetophenone, and o-nitroanisole. The reagents are used in the ratio I2 A1C13 CuCl2 = 0.5 1 1. 

Tetrafluoropyridyl organometallic reagents can be prepared by reaction of 4-bromotetra-fluoro- or tctrafluoro-4-iodopyridine with zinc or cadmium in dimethylformamide at room temperature.83 Metathesis of these reagents with copper(l) bromide affords the (2.3,5,6-tetra-fluoro-4-pyridyl)copper reagent. The latter species undergoes high-yield substitution reactions with allyl halides, vinyl iodides, aryl iodides, and alkanoyl halides. 

Demethylation of acid-sensitive aryl methyl ethers, such as 2,4-dimethoxyquinolines, can be accomplished using a trimethylsilyl iodide/DMAP reagent system, where DMAP is used as a Lewis base to prevent protonation of the alkene from the HIby-product. This reaction was utilized to form the quinoline-containing alkaloid natural product, atanine, from the Rutaceae family. 

The chelation assistance by an 8-aminoquinoline moiety mentioned above is also effective for a sp C-H arylation or allylation (Scheme 14.56). In the arylation reaction, both aryl iodides and bromides can be employed as arylation reagents, but the bromides often led to lower yields. " In the allylation reaction, only primary allyl halides can be employed. Allyl iodides gave the best results. However, when Csl was used as additive allyl iodides can be replaced with allyl bromides or chlorides. Both reactions are highly selective for the sp C-H bonds of methyl groups rather than methylene C-H bonds. 

A chelation-assisted mthenium-catalyzed arylation of aldehyde 99 was accomplished in combination with a palladium complex [47]. This cooperative catalysis [48] proved applicable to organostannanes and aryl iodides as arylating reagents (Scheme 9.35). The direct arylation proceeded most likely through ruthenium-catalyzed C—H bond activation, subsequent transmetallation to palladium, and reductive elimination from a palladium intermediate. 

Pd"" -Catalyzed Direct Arylations Synthetic Scope Aryl iodides, aryl stannanes, and aryl iodonium reagents have all been successfully employed for the direct conversion of -Ar-H -Ar Ar Pd catulytic cyclcs. For example, the Pd-catalyzed reaction of naphthalene with PhSnClj in the presence of CuCl affords the phenylated product in modest yield as a mixture of the a/p isomers (Scheme 24.9) [13]. This transformation can be applied toward the phenylation of other electron-neutral arenes, albeit, with poor efficiencies. Interestingly, reactions of naphthalene and xylenes yield products via preferential arylation of the more steri-cally hindered C—H bond. Preliminary mechanistic studies suggest a Pd" catalytic cycle for these reactions. 

Aryl iodides as reagents 17, 629 a-Arylketones 17, 868 Arylmercaptans, G-alkylation 16, 772... 

Indol-2-ylcopper reagents can also be prepared from 2-lithioindoles and they have some potential for the preparation of 2-substituted indoles. 1-Methyl-indol-2-ylcopper can be prepared by reaction of 2-lithio-l-methylindole with CuBr[10]. It reacts with aryl iodides to give 2-aryl-1-methylindoles. Mixed cyanocuprate reagents can be prepared using CuCN[ll], The cyan-ocuprate from 1-methylindole reacts with allyl bromide to give 2-allyl-l-methylindole. 

Organolithium reagents (Section 14 3) Lithi um metal reacts with organic halides to pro duce organolithium compounds The organic halide may be alkyl alkenyl or aryl Iodides react most and fluorides least readily bro mides are used most often Suitable solvents include hexane diethyl ether and tetrahy drofuran... 

Formation of aryl Grignard reagents (Section 14 4) Aryl halides react with magnesium to form the corresponding arylmagnesium halide Aryl iodides are the most reac tive aryl fluorides the least A similar reaction occurs with lithium to give aryllithium reagents (Section 14 3)... 

Aromatic perfluoroaLkylation can be effected by fluorinated aUphatics via different techniques. One category features copper-assisted coupling of aryl hahdes with perfluoroalkyl iodides (eg, CF I) (111,112) or difluoromethane derivatives such as CF2Br2 (Burton s reagent) (113,114), as well as electrochemical trifluoromethylation using CF Br with a sacrificial copper anode (115). Extmsion of spacer groups attached to the fluoroalkyl moiety, eg,... 

BURTON Trilluoromelhylation Tnfluoromethylation of aryl iodides with Cd (Cu) reagents... 

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