A method for manufacturing a compound represented by the formula (9) is provided: wherein R 2 represents a C 1 -C 4 alkyl group, R 3 represents a C 1 -C 6 alkyl group, R 4 and R 5 , independently from each other, represent a hydrogen atom, a C 1 -C 6 alkyl group or a phenyl group, or R 4 and R 5 together form a tetramethylene group, a pentamethylene group or an oxo group, and Ac represents an acetyl group.
