Halogenopyrazines reactions

Table 4 Suzuki and Suzuki-Miyaura coupling reactions of halogenopyrazines...

With the exception of those halogenopyrazines made by primary synthesis (see Chapters 1 and 2), most chloropyrazines have been made recently by the reaction of tautomeric pyrazinones with a phosphorus chloride or by the reaction of pyrazine iV-oxides with phosphoryl chloride in contrast, most other halogenopyrazines have been made by direct halogenation or by transhalogenation of chloropyrazines. A single interesting example of the conversion of a methoxy- into a chloropyrazine is included at the end of Section 4.1.1. 

The conversion of halogeno- into alkyl- or arylpyrazines has been discussed in Section 3.2.1.2. The other important reactions of halogenopyrazines are summarized in the following subsections. 

Halogenopyrazines undergo the occasional ring fission or rearrangement as well as a variety of useful cyclocondensations to afford annelated derivatives. Such reactions are typified in the following examples ... 

The important conversion of pyrazinones into halogenopyrazines has been covered in Section 4.1.1. An unusual aminolytic cyclization has been reported709 and other reactions are discussed in the subsections that follow. 

Some reactions of aminopyrazines have been discussed already the conversion of primary amino- into halogenopyrazines (Sections 4.1.4 and 4.3.2) and the conversion of aminopyrazines into pyrazinones (Section 5.1.1). The many remaining reactions are covered in the subsections that follow. 

Examples have been given already of the preparation of isothiocyanatopyrazines from halogenopyrazines (Section 4.4) or from pyrazinamines (Section 7.3.2.4) also of the reaction of isothiocyanatopyrazines with amines to give thioureidopyrazines (Section 7.3.2.4). 

The primary syntheses of pyrazine JV-oxides from aliphatic components only are described in this chapter. The preparations of pyrazine JV-oxides by oxidation of pyrazines are dealt with under the reactions of the appropriately substituted pyrazines for example, those of pyrazine and alkylpyrazine TV-oxides are described in Chapter IV, and of halogenopyrazine JV-oxides in Chapter V. The cleavage of JV-oxides of pteridines and related systems to aminopyrazine JV-oxides is described in Section VIII.3A(2). 

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