Synthesis of chiral 2,5-bis(oxazolinyl)thiophenes and their application as chiral shift reagents, for 1,1′-bi-2-naphthol

A series of C-2-symmetricai chiral 2,5-bis(4'-alkyloxazolin-2-yl) thiophenes (thiobox) have been synthesized from thiophene-2, 5-dicarboxylic acid by sequential amidation with a chiral ethanolamine, conversion of hydroxyl to chloro group, and base-promoted oxazoline ring formation. As demonstrated by (-).2, 5-bis [4'-(S)-isopropyloxazolin-2-yl] thiophene, these thiobox systems exhibited remarkable chirality recognition of 1,1'-bi-2-naphthol giving rise to pronounced shifts in the H-1 MM signals of the latter axial chiral compound at the positions of C-3, C-49 C-5, and C-8.