Orochimaru has become obsessed with Sharingan ever since loosing to Itachi.
Sadly, the only other Uchiha alive that remained in the world was Sasuke.
There is Obito, but Orochimaru doesn't know that.
Orochimaru didn't merely wanted Sharingan. He has lots of those eyes.
Sadly, Shin has disappeared when Orochimaru was weak and distracted after loosing to Itachi, and he hasn't been able to track him down yet.
So, Sasuke is the best vessel for him right now. If not for not having the dangers of being an ANBU that Itachi faced, Sasuke is probably as talented as Itachi.
3 tomoe Sharingan.
Creating Rasengan by himself.
Even his girlfriend is very talented. Talented enough to learn Rasengan and medical ninjutsu at such a young age.
But, that's why Orochimaru is troubled too.
Since Sasuke is as talented as Itachi, there is a very high chance of him awakening Mangekyo Sharingan. And though Orochimaru is confident of taking over a 3 tomoe Sharingan Sasuke, same isn't the case with Mangekyo Sharingan.
So, he can't kill Sakura.
On the other hand, as long as Sakura is alive, Sasuke probably wouldn't break enough mentally to become his perfect vessel.
So, before Sasuke becomes too strong, it is best to kidnap him, try to erase his memories with drugs, and then take over his body without any interference from Sakura.
Thankfully, Danzo stupidly believed Orochimaru's lie that he wants to kill Itachi's brother because Itachi, despite being just 13, humiliated him.
Danzo was almost too happy not having to be the one to eliminate Sasuke and Itachi hunting down Orochimaru instead.
He immediately revealed Sasuke's first mission outside the village.
'No wonder he will never become Hokage.'
Orochimaru mocked Danzo in his mind, and smirked as both Kakashi and Sasuke noticed him and froze. And then, so did Naruto and Sakura.
Kakashi immediately shouted, "We are abandoning this mission. Take Tazuna and we are running back to Land of Fire!"
"Kukuku! That's a smart decision Kakashi.
I guess you have grown up quite nicely. When you were in ANBU, you actually pursued me."
Orochimaru remembered when a 15 year old Kakashi, who Orochimaru underestimated, injured him with a paper bomb while he was escaping from Konoha.
Thinking back at it, he lost to Itachi because he underestimated him. If he had used Edo Tensei from the beginning and properly prepared instead of attacking on the first opportunity when he was alone with Itachi, things might have turned out differently.
So this time, Orochimaru was serious. He will not underestimate his opponents.
The chances of Sasuke willingly joining him is very low because of Sakura.
So he won't ask nicely.
"Hey Orochimaru! Can you take me under your wing!?"
"Wha-!?"
Just as Orochimaru was surprised by Sasuke shouting that, crows appeared everywhere.
'Itachi!?'
Orochimaru looked around, and saw Itachi calmly looking at him, his Sharingan staring into his soul.
"We finally found you, Orochimaru."
Kisame, who was with Itachi, grinned.
Orochimaru looked back at where Team 7 was, and they had disappeared.
Orochimaru also started running away.
'That damned Danzo set me up!'
Just to be sure, Orochimaru flared his chakra, scared that he might already be under Itachi's genjutsu.
The scenery suddenly shifted, and he was standing back at the first place where he was.
There were no signs of Itachi and Kisame. But, Team 7 has ran away.
"Kuku...kukukuku!"
Orochimaru laughed madly.
Sasuke has fooled him with genjutsu!
And such a genjutsu wouldn't be possible without knowing that Itachi and Kisame are partners. And that he is scared of Itachi.
How did Sasuke know that?
He licked his lip.
"You are really interesting, Sasuke-kun."
Now he was really curious.
And because of that, he started chasing Team 7.