Table 1.

Key structure of target compounds.

Compound	R1	R2	R3
5b	H	Cl	Et
6a	H	H	H
6b	H	Cl	H
6c	F	Me	H
6d	F	H	H
6e	F	Br	H
7a	H	Cl	Me
7b	H	Cl	i-Pr