You can also try Advanced ASIC Chip Synthesis Using Synopsys® Design Compiler® Physical Compiler® and PrimeTime®
by Himanshu Bhatnagar or the user guides of Synopsys to learn about synthesis.
You can download it from the forum as also other books about VHDL
a lot of tutorials about vhdl rtl synthesis, you can find those on internet. synopsys doc 'coding style for synthesis' is also a good reference for you.