Process for preparing imidazopyran derivatives

A process for preparing an imidazopyran derivative of the following formula (9),

• wherein R1 is halogen atom, hydrogen atom, C1–C3 alkyl group, aryl group, or C1–C3 alkyl group substituted by aryl group,
• which comprises reacting dinitroimidazole of the following formula (1),
• wherein R1 is the same as defined above,
• with 2,3-epoxy-1-propanol of the following formula (2),
• in the presence of a fluoride salt to prepare a diol compound of the following formula (3),
• wherein R1 is the same as defined above,
• reacting this compound (3) with a silyl halide of the following formula (4),
• R2R3R4SiX (4)
• wherein R2, R3 and R4 are independently C1–C6 alkyl group, aryl group or C1–C3 alkyl group substituted by aryl group, and X is halogen atom in the presence of a base to prepare a compound of the following formula (5),
• wherein R1, R2, R3 and R4 are the same as defined above,
• reacting this compound (5) with a compound of the following formula (6),
• R5COY (6)
• wherein R5 is aryl group or C2–C4 alkenyl group substituted by aryl group, and Y is hydroxy group, halogen atom or alkoxy group,
• to prepare a compound of the following formula (7),
• wherein R1, R2, R3, R4 and R5 are defined above,
• desilylating and cyclizing this compound (7) to prepare a compound of the following formula (8),
• wherein R1 and R5 are the same as defined above,
• and then deprotecting this compound (8) in the presence of metallic catalyst to prepare above imidazopyran derivative (9).