Synthesis of (S)-(-)- and (R)-(+)-1,5-Dimethyl-4-phenyl-1,5-dihydro-2H-pyrrol-2-ones by Carbene Ring Contraction-Decarboxylation of (2R,3R)-(-)- and (2S,3R)-(+)-Diazo-3,4-dimethyl-2-phenyl oxazepane-5,7-dione