One of Greater Boston's vast asphalt deserts in Dedham is about to be turned into what developers hope will be a suburban oasis. A 28-acre site near the intersection of routes 128 and 1 that mainly hosts a sprawling parking lot and a few scattered buildings, including a multiplex cinema, is set to become the first so-called ''lifestyle center" shopping plaza in Boston's inner suburbs. The project is carried out by Sumner Redstone's National Amusements joined with Chestnut Hill developers S.R. Weiner & Associates and is expected to be finished be autumn 2007. Soon Bostoners will enjoy an upscale, open air shopping center with about 70 specialty stores, seven or eight fine restaurants, and a 16-screen movie theater. The new center could also change the retail image of that stretch of Route 1, or Providence Highway, which lacks the cachet of Chestnut Hill's Route 9 or Braintree's South Shore Plaza.