Reactions of nucleophilic carbenes with enols

Δ3-1,3,4-Oxadiazolines.† Versatile sources of reactive intermediates

“…Oxadiazolines have been used to alkylate enols, which probably react by protonation of the carbene, subsequent ion-pair collapse to carbon of the enolate, and loss of alcohol (Scheme 31). 115 Alcohols and phenols afford the appropriate orthoformates, including members in which the orthoformyl carbon is a stereocentre (Scheme 32).…”

O-Heterocycles from Unsaturated Carbonyls and Dimethoxycarbene

“…Dimethoxycarbene 2 in particular has been reacted with carbonyls or thiocarbonyls to give α-hydroxyesters 8 or episulfurs 10 , respectively . It was also reacted with alkenes, alkynes, or isocyanates, and its reaction with vinyl isocyanates 11 or silylated bis-ketenes 13 gave cyclopentadiones 14 or lactams 12 , respectively (Scheme ). Dimethoxycarbene 2 is easily generated from the thermolysis of Warkentin’s oxadiazoline 1 in toluene at 110 or 150 °C .…”

Intermolecular Reactions of a Foiled Carbene with Carbonyl Compounds: The Effects of Trishomocyclopropyl Stabilization

“…For example, stable nucleophilic carbenes are formed by flanking a divalent C atom with two N atoms. 17, [55][56][57][58][59][60][61][62][63] 8…”

“…The n-orbital of a non-ylidic nucleophilic carbene should initiate such an elementary step with just the C atom of carbonyl compounds RC(O)R' [71][72][73]. Indeed, the nucleophilicity of foiled carbenes is evident in the deprotonation of protic solvents 61,74,75. By this manner, carbenes 1 44 and 725,44 formally insert into the O-H bond of MeOH.…”