Shippuden 350-354 spoilers (updated)
Ok people were confused by the way I posted this last time, so I will organize it better to make it easier to understand:
Episode 351 "Hashirama Cells"
-Kakashi joins Root (or helps/participates with them), and there he meets Yamato. Root comes up with a plan to assassinate the Third Hokage.
Episode 352 "Rogue Ninja: Orochimaru"
-Kakashi is assigned to chasing down Orochimaru after he leaves the village. Danzou sends out Yamato to stop Orochimaru's pursuers.
Episode 353-354 "The Boy Named Tenzou"
-Yamato meets a girl named Yukimi, whom calls him Tenzou. It is unclear if this happens in a Yamato flashback, or the ANBU arc timeline.
Source: Episode summaries from Newtype Magazine