Since the discovery of the first stable singlet carbenes, the stabilizing role of π-donating substituents. directly bonded to the electron-deficient center (as in A; Scheme 1), have been well established. More recently, it has been shown that bis(diisopropylamino)cyclopropenylidene (B; R = /'Pr) could also be isolated, whereas B~1, which bears very bulky aryl substituents, dimerizes to give the corresponding triafulva-lene. These results clearly indicate that amino groups in the (3 position, provided they are conjugated, can also stabilize electron-deficient centers.
展开▼
