Tertiary amines as synthetic equivalents of vinyl cations: zinc bromide promoted coupling of propargylamines with α-isocyanoacetamides to give 2,4,5-trisubstituted oxazoles initiated by an internal redox process.

Crabée interrupted: Propargylamines 1 react with α-isocyanoacetamides 2 in the presence of zinc bromide to afford vinyl oxazoles 3. The transformation, wherein the propargylamine acts as a vinyl cation synthetic equivalent, involves a domino sequence incorporating a 1,5-hydride shift, intermolecular trapping/cyclization, and a 1,6-elimination (see scheme).

Cu(I)-catalyzed oxidative cyclization of alkynyl oxiranes and oxetanes.

In the presence of a Cu(I) catalyst and a pyridine oxide, alkynyl oxiranes and oxetanes can be converted into functionalized five- or six-membered α,ß-unsaturated lactones or dihydrofuranaldehydes. This new oxidative cyclization is proposed to proceed via an unusual allenyloxypyridinium intermediate.

Metal-free halonium mediated acetate shifts of ynamides to access α-halo acrylamides/acrylimides.

A metal-free acetate shift of 3-acetoxy ynamides to access α-iodo, bromo, and chloro acrylamides/acrylimides under very mild conditions is demonstrated. The inherent alkyne activation of ynamides is sufficient to ensure the α-halo acrylamides/acrylimides in high yields without the addition of a catalyst. In all cases high Z-stereoselectivity is observed.

Gold(I)-catalyzed formation of dihydroquinolines and indoles from N-aminophenyl propargyl malonates.

The use of [XPhosAu(NCMe)]SbF(6) in nitromethane at 100 °C allows the rapid and efficient formation of variously substituted dihydroquinolines, which can be subsequently converted into indoles by a rare photochemical rearrangement.

Gold(I)-catalyzed rearrangement of propargyl benzyl ethers: a practical method for the generation and in situ transformation of substituted allenes.

A series of benzyl propargyl ethers react with a gold(I) catalyst to furnish variously substituted allenes via a 1,5-hydride shift/fragmentation sequence. This transformation is rapid and practical. It can be performed under very mild conditions (room temperature or 60 degrees C) using terminal as well as substituted alkyne substrates bearing a primary, secondary, or tertiary benzyl ether group. The allenes thus formed can be reacted in situ with an internal or external nucleophile, corresponding to an overall reductive substitution process, to produce more functionalized compounds.

Hydroalkylation of alkynyl ethers via a gold(I)-catalyzed 1,5-hydride shift/cyclization sequence.

A series of alkynyl ethers react with an electrophilic gold(I) catalyst to produce a range of structurally complex spiro or fused dihydrofurans and dihydropyrans via a 1,5-hydride shift/cyclization sequence. This hydroalkylation process, which is performed under practical experimental conditions, can be applied to terminal as well as ester-substituted alkynes. It allows the efficient conversion of secondary or tertiary sp(3) C-H bonds into new C-C bonds by the nucleophilic addition of a vinylgold species onto an oxonium intermediate. The stereoselectivity of the cycloisomerization process toward the formation of a new five- or six-membered cycle appears to be dependent on steric factors and the alkyne substitution pattern.

Synthesis of functionalized oxazolones by a sequence of Cu(II)- and Au(I)-catalyzed transformations.

A study concerning a two-step sequence leading to the formation of diversely 1,5-disubstituted oxazolones is described. The mild conditions employed allow the efficient and rapid synthesis of a variety of such compounds via an initial Cu(II)-catalyzed coupling of a bromoalkyne with a secondary tert-butyloxycarbamate followed by a Au(I)-catalyzed cycloisomerization of the N-alkynyl tert-butyloxycarbamates thus obtained.