Substituted pyrazines and a process for producing the same

A process for producing a compound represented by formula (VIII):

• wherein R1 is hydrogen;
• a halogen;
• an aryl which may optionally be substituted with at least one substituent selected from the group consisting of a halogen, hydroxy, an alkyl having 1 to 6 carbon atoms, an alkoxy having 1 to 6 carbon atoms, an amino and a dialkylamino having 1 to 6 carbon atoms;
• an arylalkyl which may optionally be substituted with at least one substituent selected from the group consisting of a halogen, hydroxy, an alkyl having 1 to 6 carbon atoms, an alkoxy having 1 to 6 carbon atoms, an amino and a dialkylamino having 1 to 6 carbon atoms;
• an arylalkenyl which may optionally be substituted with at least one substituent selected from the group consisting of a halogen, hydroxy, an alkyl having 1 to 6 carbon atoms, an alkoxy having 1 to 6 carbon atoms, an amino and a dialkylamino having 1 to 6 carbon atoms;
• an alkyl which may optionally be substituted with an alicyclic group;
• an alkenyl which may optionally be substituted with an alicyclic group;
• an alicyclic group;
• a heterocyclic group;
• or an alkynyl which may optionally be substituted with an alicyclic group, and
• R4 is a protecting group selected from the group consisting of methyl, methoxymethyl, tetrahydropyranyl, benzyl, 4-methoxybenzyl, tert-butyldimethylsilyl, trimethylsilyl, triethylsilyl, phenyldimethylsilyl, tert-butyldiphenylsilyl, and triisopropylsilyl,
• which comprises:
• (1) reacting 2-amino-3,5-dibromo-6-chloropyrazine with R1MgX and ZnCl2, wherein R1 is the same as defined above and X is a halogen, in the presence of a palladium catalyst to give a compound represented by formula (V):
• wherein R1 is the same as defined above;
• (2) reacting the compound represented by formula (V) with a compound represented by formula (VI):
• wherein R4 is the same as defined above, in the presence of a palladium catalyst and a base to give a compound represented by formula (VII):
• wherein R1 and R4 are the same as defined above;
• and,
• (3) reacting the compound represented by formula (VII) with tributyl(vinyl)tin in the presence of a palladium catalyst to give the compound represented by formula (VIII).