Halides, aryl, arylation synthesis

Boger and co-workers were the first to report the intramolecular amination of aryl halides in their synthesis of lavendamycin [436-438], Thus, biaryl 366 is smoothly cyclized under the action of 1.5 equivalents of Pd(PhjP)4 to P-carboline 367, which comprises the CDE rings of lavendamycin. 

As with most organic halides, aryl halides most often are synthetic intermediates for the production of other useful substances. For example, chlorobenzene is the starting aryl halide for the synthesis of DDT it also is a source of benzenol (phenol, Section 14-6C) which, in turn, has many uses (Section 26-1). 

The following shows the method of preparing and using magnesium aryl halides in this synthesis. 

Reactions with Aryl Halides and Inflates Synthesis of Biaryls... 

Although isocyanates have been known tor some time, the isomeric cy-anates were unknown until 1964 The latter were first prepared almost simultaneously by two different methods (1) thermolysis of 5-aryl- or 5-alkyloxy 1,2,3,4-thiatnazoles and (2) by reaction of phenols or alcohols with cyanogen halides Since their synthesis, cyanates have ac-... 

The first application of arylstannanes was presented by Stille who demonstrated the transferability of an aryl group from tetraphenyltin [50]. This approach was generalised by the improved preparation of arylstannanes from trialkylstannanes and aryl halides followed by their Pd(0) catalysed coupling with aryl halides [51]. Similarly to aryl halides, aryl triflates also react with arylstannates to give biphenyls [52]. Electron-rich aryl triflates are especially suitable coupling reagents in the synthesis of unsymmetrical biaryls [53]. Symmetrical biaryls can be easily obtained by the reaction of an aryl triflate with 0.5 eg. of hexamethyldistannane. 

A well-established method for the synthesis of internal alkynes 34 is the Pd/Cu-catalyzed coupling of vinyl halides, aryl iodides, bromides, or triflates with terminal acetylenes 33 (Scheme 12). Nevertheless, this method suffers not only from the need for large amounts of catalyst (1-5 mol % Pd and 1-10 mol % Cul) but also from the need of higher temperatures for the aryl bromides. 

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