Halogen-dance oxidative

Oxidative dimerization of A,A-dialkyl-<9-(8-lithio-7-quinolyl)carbamates with anhydrous ferric chloride has been shown to be efficient for the preparation 1,1 -dioxygenated 8,8 -biquinolyls (Scheme 61) and it is anticipated that this tandem halogen-dance oxidative dimerization reaction will find further applications for the synthesis of other highly substituted biaryl molecules.96... 

Oxidation of thiophene with Fenton-like reagents produces 2-hydroxythiophene of which the 2(570 One isomer is the most stable (Eq. 1) <96JCR(S)242>. In contrast, methyltrioxorhenium (Vn) catalyzed hydrogen peroxide oxidation of thiophene and its derivatives forms first the sulfoxide and ultimately the sulfone derivatives <96107211>. Anodic oxidation of aminated dibenzothiophene produces stable radical cation salts <96BSF597>. Reduction of dihalothiophene at carbon cathodes produces the first example of an electrochemical halogen dance reaction (Eq. 2) <96JOC8074>. 

While 5-chloro-l,2,3-triazole 1-oxide 467 reacted with sodium methox-ide with replacement of the chlorine (see Section 4.1.6.8), the corresponding bromo compound 468 under similar conditions afforded the cme-substitution product 483 as the main product (1987ACSA(B)724). A mechanism involving halogen dance and supported by control experiments is sketched in Scheme 142. The bromine in 468 is located at the less activated position with respect to nucleophilic displacement. On the other... 

The pyridine 122 reacts with BuLi by I/Li exchange capture of the lithium derivative with propanal and oxidation gives the ketone 130 in the heterocyclic equivalent of a Friedel-Crafts acylation. The fluorine atom that was originally present to initiate the halogen dance from 120 to 121 can now be hydrolysed to give the pyridone 126. 

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