I2C - RS232 controller
NXP make a range of I2C to UART bridge chips, http://ics.nxp.com/products/bridges/i2c.spi.slave.uart.irda.gpio/

http://ics.nxp.com/products/bridges/i2c.spi.slave.uart.irda.gpio/images/use.remote.gif

Have a look at the SC16IS740.