A wave of spectacular new developments is poised to transform and enlarge the top end of Manhattan’s office market, even as many older and underperforming buildings undergo conversion to apartments. Some are already in early construction, others with signed anchor tenants are poised to go vertical,  and yet others are  awaiting the magic cocktails of anchor tenants and financing to proceed.  JLL’s New York chairman and president Peter Riguardi,  a prolific dealmaker in his own right, put the