Indolizine compounds and method for the synthesis thereof

A method for synthesizing a compound represented by the formula (IV):

• comprising the steps of:
• metalating an indolizine not having a substituent at the 5-position with a metal compound and,
• reacting it with a boric acid ester compound,
• wherein R21 to R26 independently represents a substituent selected from the group consisting of hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthio group, a substituted or unsubstituted arylthio group, a substituted or unsubstituted alkylamino group, a substituted or unsubstituted arylamino group, a substituted or unsubstituted alkylcarbonyl group, a substituted or unsubstituted arylcarbonyl group, a substituted or unsubstituted alkylsulfonyl group, a substituted or unsubstituted arylsulfonyl group, a substituted or unsubstituted alkoxycarbonyl group, a substituted or unsubstituted aryloxycarbonyl group;
• a substituted or unsubstituted alkylcarbamoyl group, a substituted or unsubstituted arylcarbamoyl group, a substituted or unsubstituted alkylsulfamoyl group, a substituted or unsubstituted arylsulfamoyl group, a substituted or unsubstituted alkylcarbonyloxy group, a substituted or unsubstituted arylcarbonyloxy group, a substituted or unsubstituted alkylcarbonamido group, a substituted or unsubstituted arylcarbonamido group, a substituted or unsubstituted alkylsulfonamido group, a substituted or unsubstituted arylsulfonamido group, a substituted or unsubstituted urethane group, a substituted or unsubstituted ureido group, a substituted or unsubstituted carbonic acid ester group, the substituents selected from R21 to R26 may combine with each other to form a cyclic structure, R27 and R28 each represents hydrogen atom, an alkyl group, an aryl group or a heterocyclic group, and R27 and R28 may combine with each other to form a cyclic structure.