Development of the Scope of a Co-Mediated O→C Rearrangement Reaction

Gold(i) catalyzed [1,3] O → C rearrangement of benzylvinyl ethers

A simple procedure for the preparation of 3-(hetero)arylpropionaldehydes has been developed employing a gold-catalyzed [1,3]-rearrangement of vinyl ethers.

Cyclic α-Alkoxyphosphonium Salts from (2-(Diphenylphosphino)phenyl)methanol and Aldehydes and Their Application in Synthesis of Vinyl Ethers and Ketones via Wittig Olefination

Cyclic α-alkoxyphosphonium salts have been synthesized from (2-(diphenylphosphino)phenyl)methanol and aldehydes in 36-89% yields. These phosphonium salts are bench-stable solids and undergo Wittig olefination with aldehydes under basic conditions (K2CO3 or t-BuOK) to form benzylic vinyl ethers, which are readily hydrolyzed to 1,2-disubstituted ethanones under acidic conditions. The formation mechanism of these phosphonium salts via hemiacetal is also proposed.

Gold(i)-catalysed [1,3] O→C rearrangement of allenyl ethers

Gold standard: a simple and rapid access to the α-substituted acryl aldehydes has been provided by developing a gold-catalysed [1,3] rearrangement of the allenyl ethers importantly with a record turnover frequency = 4600 h⁻¹ (at 0.05 mol% of the catalyst concentration) in homogeneous gold(i) catalysis.

The [1, 3] O-to-C rearrangement: opportunities for stereoselective synthesis

The relay of stereochemistry of a breaking C-O bond into a forming C-C bond is well-known in the context of [3, 3] sigmatropic shifts; however, this useful strategy is less well-known in other types of molecular rearrangements. Though the first successful example of a [1, 3] O-to-C rearrangement was reported more than 100 years ago, this class of reactions has received less attention than its [3, 3] counterpart. This perspective analyzes the various methods used for the activation and [1, 3] rearrangement of vinyl ethers with an emphasis on mechanism and applications to stereoselective synthesis. We also highlight our own contributions to this area.

Investigation of the Scope of a Co-Mediated O → C Ring-Contraction

A series of dihydropyrans bearing a dicobalthexacarbonyl moiety have been found to undergo an efficient Al-promoted O-->C ring-contraction process. This rearrangement reaction operates successfully for a broad range of substrates. Moreover, the potential of this approach for generating cyclopropanes from the corresponding dihydrofurans has been demonstrated.

Development of a Stereoselective Co-Mediated Dihydropyran Ring Contraction

A highly stereoselective approach for the synthesis of trans-1,2-disubstituted cyclobutanes through an Al-promoted cobalt-mediated O-->C ring contraction of dihydropyrans is described. [reaction: see text].