Victor Sigoura’s Legion Investment Group is advancing its luxury condo project near Gramercy Park with a $72 million deal for a four-parcel assemblage along Third Avenue. The purchase of 252-258 Third Avenue, including air rights from a neighboring co-op building, brings Sigoura closer to acquiring a coveted key to Gramercy Park. To unlock the private garden’s gates, he needs to complete the project and purchase the neighboring co-op building at 38 Gramercy Park North, which is expected to make it the largest new development project along Gramercy Park in over a decade