Cyclopropenylidenephosphoranes: Rearrangement to Azetidinylidene-Methylphosphoniums.

Attempts at preparing cyclopropenylphosphonium salts by P-quaternization of α-aminophosphines with bisdiisopropylaminocyclopropenium tetrafluoroborate led to azetidin-2-ylidene methylphosphoniums as unexpected isomers, in 57-85% yields. The basic structure of the products is discussed on the basis of X-ray crystallography analysis. The unprecedented 3 → 4 ring expansion process is argued to be driven by an ambivalent aromatic vs antiaromatic character (or loss of aromaticity) of the primary phosphonium product.

Transition-Metal-Free α-Vinylation of Enolizable Ketones with β-Bromostyrenes.

An α-vinylation of enolizable ketones has been developed by using β-bromostyrenes and a KO tBu/NMP system. β,γ-Unsaturated ketones of E configuration were obtained in excellent yield and selectivity. Further synthetic possibilities are highlighted by one-pot functionalization via trapping of intermediate dienolates with alkyl, allyl, benzyl, and propargyl halides to generate quaternary centers.

Phosphenium Versus Pro-Phosphide Character of P-tert-butyl-dicyclopropeniophosphine: Zwitterionic Palladate Complexes of a Dicationic Phosphido Ligand.

With the view to enhancing the unique coordinating ability of the known phenyl-tetrakis(diisopropylamino)dicyclopropeniophosphine (Ph-DCP), replacement of the phenyl substituent by a tert-butyl substituent was envisaged. Both α-dicationic R-DCP phosphines, with R = Ph and Bu, were prepared in 54%-55% yield by substitution of RPCl with two equivalents of bis(diisopropylamino)-dicyclopropenylidene (BAC) and metathesis with NaBF. This method is implicitly consistent with the representation of R-DCPs as BAC-phosphenium adducts.