The 22-year-old has moved to the Keepmoat Stadium as part of the £500,000 deal plus add-on payments which has seen left-back James Husband join Boro.
Main’s arrival follows Rovers’ capture of Nathan Tyson on a one-year deal with Rovers boss Paul Dickov now expected to try and seal a move to re-sign fans favourite James Coppinger.
On Main, Dickov, who has also completed the signing of trialist left-back Cedric Evina on a 12-month contract as a direct replacement for Husband, said: “He’s big, strong and quick.
“The one thing you will get off him is 110 per cent every game and he gives us a different option.
“There are a lot of goals in him and he is very hungry and very focussed and he is the type of player we want to bring in.”
“We look at players and get to know them as people and Nathan (Tyson) and Curtis, along with Theo (Robinson), will be real assets for the division we are going in to.”
Leeds United say they have ended their interest in Chesterfield centre-half Liam Cooper, with the club having also paved the way for Tom Lees to join Sheffield Wednesday.
No fee is likely to be involved in Lees’ impending move.
Chesterfield chief executive Chris Turner confirmed the club have turned down a bid for former Hull City defender Cooper, understood to be in the region of £475,000, and Leeds have now said their interest in the player is over.
Turner said: “We have turned down an initial bid which was below our valuation of Liam and we now await a response from Leeds.
“I am not surprised that there has been interest in Liam because he is a quality player.”