The compound according to claim 1, wherein R1 and R2 represent C1-4 alkoxy, R3 represents a group other than a hydrogen atom, R4, R5, and R6 represent a hydrogen atom, and A represents group (ii) wherein j is 1 or 2, k is 1 or 2, m is 1 or 2, and R15 represents optionally substituted phenyl. 14.