Diastereoselective Synthesis of Trans-2,3-Diaryl(Heteroaryl)-3,6-Dihydropyrans by an Allylboration/Ring-Closing-Metathesis Sequence

trans-2,3-Diaryl(heteroaryl)-dihydropyrans were synthesized by an allylboration/ring-closing-metathesis sequence, using allylboranes formed in situ from the corresponding allylic alcohols. Aryl(heteroaryl) substituents were thus installed diastereoselectively onto dihydropyran rings in a trans fashion. These disubstituted dihydropyrans were further transformed into monosaccharide-like tetrahydropyrans.