For decades the western end of 42nd Street has been the dark corner of Midtown, a place shunted to the side and left for squalor as the engines of commerce and progress rolled by.

Cora Cahan, president of the New 42nd Street, a nonprofit organization established by New York State and New York City that is charged with revitalizing the area’s theaters, remembers a time when a parking lot at the corner of 42nd Street and 8th Avenue was at its busiest between the hours of 2:45—5:30 a.m., when people looking for drugs or prostitutes stopped in for a few moments at a time.

While “the Deuce” fitfully shed its peep shows and penny arcades in favor of Virgin megastores and Bubba Gump’s Seafood Co., that corner stayed in the shadows. Even the parking lot was abandoned and fell into disuse, taken over by trash and urban flora.

That changed earlier this month, when ground was broken at the site for 11 Times Square, a glittering new high-tech skyscraper designed by FXFowle for SJP properties, a New Jerseybased developer of suburban office parks.

“If you collapse time, the idea that this site is now going to be an architect-designed office building is really quite remarkable,” said Ms. Cahan. “All those ‘re-‘ words that we have used to talk about 42nd Street for so long — renew, restore, repair — we are really going to have to stop using them. The entire block has been reinvented.”

The building, a 600-foot, 40-story tower, features sculptural forms covered in a sheer glass curtainwall and silk-glass spandrel panels, and is expected to achieve LEED silver certification from the U.S. Green Building Council. It is expected to cost more than $1 billion to construct, according to a spokesman for SJP Properties, Fred Feiner, and will be finished by fall 2009.

The chief designer for the project, Robert Kaplan, said he wanted the building to be a part of its schizophrenic surroundings, incorporating both the delirium of the new Times Square and the sober business district to its south. The southern side of the building, which Mr. Kaplan calls “the corporate side,” is rectilinear and modern; the northern front he calls “a jumble of fragments that adds to the sprit and energy of Times Square.” It features several large signage “spectaculars” and a 40-foot in diameter globe in one corner.

“When you do something in Times Square you have to make sure, especially at the base, that it’s strong enough to compete, that it can accept the inevitable variation of many different layers and signs that are happening,” he said.

The parcel the building will occupy is the last buildable site on 42nd Street. SJP acquired the land for $306 million in September 2006 from Howard and Edward Millstein. It is envisioned as capstone on the redevelopment of the area and a gateway to the “new 42nd Street,” according to Ms. Cahan.

“Our overriding public goal was put people on the street, and you have certainly seen that established” she said. “It is beyond the city father and state mother’s wildest expectations what has happening on that street.”

The tower will stand between the new Westin Hotel on 43rd Street and the new Renzo Piano-designed headquarters of the New York Times.

The Millsteins purchased the land in 1983 for $5 million, as part of an earlier citywide attempt to clean up the area. Their attempts to build something on the site sputtered.

The project is the first in years to be built without an anchor tenant, a sign of the increased demand for office space and symbolizing a further encroachment of the Midtown business district, real estate observers say.

“The area has come around to where it is acceptable as an office location,” the director of research for Colliers ABR, Robert Sammons, said. “Having the Port Authority across the street is something of a problem, but I think this is going to be where the big growth of Manhattan takes place over the next 25 years.”

Ms. Cahan concurs: “Midtown is marching to the east. It’s like there is a parade, you can feel the buildings coming toward. The vibrancy and vitality of the city is palpable in that area.”