Furans, 2-aryl-, halogenation

Chlorine, Antimony trichloride, Tetramethylsilane, 4047 Chlorine, 2-Chloroalkyl aryl sulfides, Lithium perchlorate, 4047 Sulfur tetrafluoride, 2-(Hydroxymethyl)furan, Triethylamine, 4350 Titanium, Halogens, 4919... 

An unexpected deshielding is found in 2-halogenoaryl furans such as (112) where the adjacent proton is noticeably affected (Table 6). No other substituent behaves like this, and halogens in other positions are likewise devoid of effect. Perhaps for some reason the conformation is preferred that has the halogen atom close to the proton. This would help to explain the fact that a second halogen atom at the aryl 6-position restores the resonance to its normal position, and that the effect is temperature dependent (71NKK1206). 

Since halogen-substituted benzo[. ]furans play an important role in the transition metal-catalyzed coupling of benzo[. ]furans with other substrates, synthetic methods to regioselectively synthesize substituted benzo[ ]furan halides have become very critical routes. Several syntheses of benzo[ ]furan based aryl halides are described here. 

Solvolyses data for 5-substituted 2-furylmethanol derivatives have been correlated.446 Results for arylation fit Hammett plots using a+ values provided that the aryl radical contains strongly polar substituents such as nitro or halogen.4461 Another correlation involves eliminations in 1 -(2-furyl)-ethyl acetate to give furyl alkenes.447 The furan ring itself has been assigned a a value.4-146... 

The reactions of a-halo-substituted fluorine-containing furans with nucleophilic reagents ° ° are the most studied reactions proceeding with participation of halogen atoms. A fluorine atom in 2-fluoro-3-trifluoromethyl-5-aryl-furans 224 is replaced smoothly by various nucleophiles.The similar reactions were reported for 2-fluoro-3 -trifluoromethyl-5 -aryl-thiophenes. ... 

In studies whose thrust is the development of the new O-sulfamate DMG, orf/zo-bromo aryl 0-sulfamates are subjected to metal-halogen exchange in the presence of furan (eq 56) to give, following treatment with catalytic HCl, naphthol derivatives. The TMS substituent is cleaved by protodesilylation under these conditions. 

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