Can I use shimano 6700 chain rings on my shimano 7400 crank set? I am upgrading the drive train and would like to keep the crank if possible.
See this answer.
So long as the BCD (bolt circle diameter) and bolt pattern (4 bolts, 5 bolts) matches up between the cranksets, you can swap rings between cranksets.
For example, if you have the Ultegra compact and got the Dura-ace regular double, the BCD's will be different and you can't swap them. However, if they are both compact or both regular doubles, they will have the same BCD's and you can swap the chainrings.
Some may complain about possibly different chainring widths, but in practice between 10 and 11 speed you wouldn't notice the difference (if there is any).