Catalyst-directed diastereoselectivity in hydrogenative couplings of acetylene to alpha-chiral aldehydes: formal synthesis of all eight L-hexoses.

Hydrogenative coupling of acetylene to alpha-chiral aldehydes 1a-4a using enantiomeric rhodium catalysts ligated by (S)-MeO-BIPHEP and (R)-MeO-BIPHEP delivers the diastereomeric products of carbonyl-(Z)-butadienylation 1b-4b and 1c-4c, respectively, with good to excellent levels of catalyst directed diastereofacial selectivity. Diastereomeric L-glyceraldehyde acetonide adducts 1b and 1c were converted to the four isomeric enoates 6b, 8b, 6c, and 8c, representing a formal synthesis of all eight L-hexoses.