(( Is it possible to use CYGNAL F002 as a master in I2C full speed (400kHz) net?))

Yes it is.
You can even obtain 1MHz bit rate on SMBus with a 20MHz system clock for CYGNAL F002
If your controller is a “single master” on the bus you can implement a “bit bang” technique with a common 8051/52 like uC because the master protocol is simpler then the slave protocol. As a “single master” you may bypass the collision problem.

Regards,
Cristian