Sometimes, Mac user face the situation where iTunes can't see connected iPhone, iPod, or iPad. I just have faced this problem when migrating from iMac to MacBook. iTunes on my MacBook can't see my iPhone. So, I can't sync up. Even, I have migrated iTunes library from iMac to MacBook.
Common problem is about the driver, AppleMobileDevice.kext. The solution is simple, just reinstall the iTunes. But, sometimes we need more than that. Make sure you have administrator rights, and over Terminal.app type:
sudo rm -rf /System/Library/Extensions/AppleMobileDevice.kext