Zirconium-Catalyzed Hydroalumination of C═O Bonds: Site-Selective De-O-acetylation of Peracetylated Compounds and Mechanistic Insights.

An unprecedented hydroalumination of C ═ O bonds catalyzed by zirconocene dichloride is reported herein and applied to the site-selective deprotection of peracetylated functional substrates. A mixed metal hydride, with 1:1 zirconium/aluminum stoichiometry, is also shown to be the reductive species. A catalytic cycle is finally proposed for this transformation with no precedent in the field of zirconium catalysis.

Carbene-Mediated Quaternarization of the Anomeric Position of Carbohydrates: Synthesis of Allylic Ketopyranosides, Access to the Missing α-Gluco and ß-Manno Stereoisomers, and Preparation of Quaternary 2-Deoxy 2-Acetamido Sugars.

Following our work on the C-H functionalization of carbohydrates by the 1,5 insertion of metal-carbenes, we report herein the robust and scalable conversion of sugar γ-lactones into highly valuable glycosides having a quaternary anomeric position substituted by an allyl chain ready for further functionalization. A divergent synthetic approach furthermore provided a straightforward access to ketopyranosides with a large chemo- and stereodiversity at position 2.

Hydrozirconation/bromination, followed by a Michaelis-Arbuzov reaction, as a convenient approach towards polyfunctional glycosylphosphonates.

In this note, an hydrozirconation/bromination/Michaelis-Arbuzov sequence was developped to introduce a trimethylene phosphonate unit on ketopyranosides. Performed on polyfunctional substrates bearing orthogonal protecting groups, this new approach provided a straightforward entry towards a large diversity of glycophosphomimetics having a quaternary anomeric position.

Regio- and Chemoselective Deprotection of Primary Acetates by Zirconium Hydrides.

A combination of DIBAL-H and Cp2ZrCl2 is shown to promote the regioselective cleavage of primary acetates on a broad scope of substrates, ranging from carbohydrates to terpene derivatives, with a high tolerance toward protecting groups and numerous functionalities found in natural products and bioactive compounds. Apart from providing highly valuable building blocks in only two steps from biosourced raw materials, this selective de- O-acetylation should also be strongly helpful to solve selectivity issues in organic synthesis.