Thunderbolt Gen 1 and 2 don’t support USB 3.1, Type C or even 3.0 for
that matter. An adapter wouldn’t have fixed this problem. However,
Apple is releasing Thunderbolt 3 later in 2015. It’s not ready yet,
because it’s developed with Intel and now Gen 3’s functionality is
tied to Skylake chips – which will replace Broadwell shortly. I know.
You’re thinking “But Broadwell just came out!” That’s true, but only
because of delays. Now, you may wonder how a new MacBook without a
Thunderbolt port or a Skylake chip will support a Thunderbolt Display.
Well, in short it won’t. That is unless Apple releases a firmware
update for their Thunderbolt cables. Which they won’t. So it probably
won’t support it. Considering the last time they updated it, I think
we’ll see an update at WWDC, with a USB C port on the display itself.
link
What might be a solution is an ungodly combination of:
StarTech’s female Mini DisplayPort to male DisplayPort adapter ($4.50)
A female-to-female DisplayPort coupler ($13.50)
a DisplayPort-to-HDMI cable (as little as $6)
Apple’s $79 USB-C Digital AV Multiport Adapter, which has an HDMI port
on it in addition to pass-through USB-C power and USB Type A 3.1 for
data
link
Buona fortuna ^^