Synthetic and mechanistic studies on the antitumor antibiotics esperamicin A1 and calicheamicin .gamma.1: synthesis of 2-ketobicyclo[7.3.1.]enediyne and 13-ketocyclo[7.3.1]enediyne cores mediated by .eta.2]dicobalt hexacarbonyl alkyne complexes. Cycloaromatization rate studies