Process for producing substituted benzo[F]imidazo[1,2-A]quinoxalin-3(11H)-ones

1. A process for producing a v-coelenterazine compound represented by formula (II):

wherein:

R 1 is hydrogen; a halogen; an unsubstituted aryl; an aryl 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 unsubstituted arylalkyl; an arylalkyl 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 unsubstituted arylalkenyl; an arylalkenyl 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 unsubstituted alkyl; an alkyl substituted with an alicyclic group; an unsubstituted alkenyl; an alkenyl substituted with an alicyclic group; an alicyclic group; a heterocyclic group; an unsubstituted alkynyl; or an alkynyl substituted with an alicyclic group,

each of R 2 and R 3 independently represents hydrogen, hydroxy, a halogen, an unsubstituted alkyl having 1 to 4 carbons; an alkyl having 1 to 4 carbon atoms substituted with an alicyclic group, trifluoromethyl or an alkoxy,

which comprises:

(1) reacting a compound represented by formula (VIII):

wherein R 1 is the same as defined above; and R 4 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;

with a methyltriphenylphosphonium salt in the presence of a solvent and a base to give a compound represented by formula (IX):

wherein R 1 and R 4 are the same as defined above;

(2) performing a ring-closing metathesis reaction on any one selected from the group consisting of the compound represented by formula (IX) and a compound represented by formula (X) which is prepared by protecting the amino in formula (IX) with R 5 :

wherein R 1 and R 4 are the same as defined above; and R 5 is a protecting group selected from the group consisting of acetyl, benzoyl, p-tosyl, tert-butoxycarbonyl and benzyloxycarbonyl

in the presence of a solvent and a catalyst, and then deprotecting R 4 and, if any, R 5 to give a v-coelenteramine compound represented by formula (XIV):

wherein R 1 is the same as defined above; and,

(3) reacting the compound represented by formula (XIV) with a compound represented by formula (XV):

wherein each of R 2′ and R 3′ independently represents hydrogen, hydroxy, an alkoxy, a halogen, a hydrocarbon group, or a hydroxy group protected with a protecting group selected from the group consisting of tert-butyldimethylsilyl, methoxymethyl, tetrahydropyranyl, trimethylsilyl, triethylsilyl, phenyldimethylsilyl, tert-butyldiphenylsilyl, and triisopropylsilyl to give the compound represented by formula (II).

2. The process according to claim 1 , wherein at least one base selected from the group consisting of n-butyl lithium, potassium tert-butoxide, sodium methoxide, sodium ethoxide and lithium diisopropylamide is used as the base in step (1).

3. The process according to claim 1 , wherein at least one solvent selected from the group consisting of tetrahydrofuran, diethyl ether, cyclopropyl methyl ether, tert-butyl methyl ether, dioxane and toluene is used as the solvent in step (1).

4. The process according to claim 1 , wherein the reaction temperature and reaction time in step (1) are set at 0° C. to 40° C. for an hour to 4 hours.

5. The process according to claim 1 , wherein a second generation Hoveyda-Grubbs catalyst is used as the catalyst for the ring-closing metathesis reaction in step (2).

6. The process according to claim 1 , wherein at least one solvent selected from the group consisting of dichloroethane, dichloromethane, chloroform, trichloroethane, tetrachloroethane, benzene, toluene, xylene, monochlorobenzene, dichlorobenzene, hexane, heptane, octane, tetrahydrofuran, dioxane, diethyl ether, dibutyl ether, diisopropyl ether and dimethoxyethane is used as the solvent for the ring-closing metathesis reaction in step (2).

7. The process according to claim 1 , wherein the reaction temperature and reaction time of the ring-closing metathesis reaction in step (2) are set at 25° C. to 110° C. for an hour to 48 hours.