The strongly resonance donating methoxy group stabilizes singlet relative to triplet carbenes,'mitigates their reactivity,” and accentuates their nucleophilic~ r 0 perties. s~ Modulation or “tuning” of the electronic properties of the oxa substituent should lead to “designer” oxacarbenes of varied reactivity and synthetic utility. For example, the trifluoroethoxy group, CF3CH20, is a weaker resonancedonor (u~+-0.56) 8-~ 0than ...