Groupon CEO Andrew Mason with Mayor Richard Daley, Aug. 31, 2010. (Brian Cassella/ Chicago Tribune)

Google Inc. is reportedly closing in on a deal to buy online discount-coupon sensation Chciago-based Groupon for up to $6 billion in its largest-ever acquisition, signaling a willingness to use some of its huge cash hoard to buy growth.

A deal, reported by several media, would give Google an important window into a fast-growing $91 billion local advertising market.

But Google’s shares fell 4.5 percent, partly on concern it may shell out too much for a business likely to face increasing competition. Reports of the deal came as the European Union announced plans to investigate Google’s search practices. Get the full story »