Require a prompt before automatic syncing
If you've set up automatic syncing, iTunes syncs your iPod, iPhone, or iPad whenever you connect it. If you want iTunes to ask you before automatically syncing, you can do so.
You can have iTunes ask you before syncing a specific iPod, iPhone, or iPad; or all iPod, iPhone, or iPad devices you connect to your computer.
Require a prompt before syncing a specific iPod, iPhone, or iPad
Connect your iPod, iPhone, or iPad to your computer and select your device.
Click Summary, and then deselect “Open iTunes when this Device is connected.”
Note: This option isn’t available if you’ve selected “Prevent iPods, iPhones, and iPads from syncing automatically” in the Devices pane in iTunes preferences.
Require a prompt before syncing all iPod, iPhone, and iPad devices
In iTunes, choose iTunes > Preferences.
Click Devices.
Select “Prevent iPods, iPhones, and iPads from syncing automatically.”
To sync your iPod, iPhone, or iPad when a prompt is required, connect your iPod, iPhone, or iPad to your computer, choose your device from the Devices pop-up menu near the top of the iTunes window, and click Sync.
For more information, see the iPod, iPhone, or iPad User Guide or the Apple Support website.