Patent ID: 6900204

Claim:
A compound of formula I: wherein A 1 and A 2 combine to form a fused ring described by formulas: X 1 represents an oxygen atom. R 1 represents H, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 -alkynyl, aryl, or heteroalkyl; R 2 represents OR 3 , SR 3 , a hydrogen atom, or an alkyl group having 1 to 3 carbon atoms; each R 3 , independently, represents H, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 -alkynyl, acyl, aryl, heteroalkyl, S(O) 1-2 —C 1-6 alkyl, S(O) 1-2 -aryl, S(O) 1-2 —C 2-6 alkenyl, or S(O) 1-2 —C 2-6 -alkynyl; and R 4 represents a group expressed by the formula: wherein each of R 5 and R 6 is, independently, an alkyl group having 1 to 7 carbon atoms, or R 4 represents a group expressed by the formula: in which g represents an integer between 1 and 3; or R 4 represents a group expressed by the formula: wherein each of R 7 and R 8 is, independently, a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and X 2 represents an oxygen atom, a sulfur atom, a carbonyl group, or X 2 represents a group expressed by the formula: in which each of R 9 and R 10 is, independently, a hydrogen atom, or an alkyl group having 1 to 3 carbon atoms, or R 9 and R 10 , in combination with each other, represent —(CH 2 ) k — in which k represents an integer between 1 and 4; or X 2 represents a group expressed by the formula: in which m represents 0 or 1, R 11 represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or —(CH 2 ) n X 3 in which n represents an integer between 1 and 4, and X 3 represents a halogen atom, an alkoxy group having 1 to 3 carbon atoms, a vinyl group, or an ethynyl group, or X 2 represents a group expressed by the formula: