From Glycals to Metal Pyranosylidenes: Diastereoselective Addition of Electrophiles to Metal Carbene Enolate Intermediates

Lithiated glucals react smoothly with Cr(CO)5THF at the metal center to generate the corresponding vinyl chromate intermediates which represent chromium carbene enolate equivalents. Trapping by electrophiles provides an entry to novel chromium 2-deoxy-pyranosylidenes. Deuteration and allylation proceed with an approximately 90% d.e. in preference of the C-2-manno complexes.