Asymmetric Diels–Alder reaction of 3-(acyloxy)acryloyl oxazolidinones: optically active synthesis of a high-affinity ligand for potent HIV-1 protease inhibitors

We describe here our investigation of the asymmetric Diels–Alder reaction of chiral 3-(acyloxy)acryloyl oxazolidinones as dienophiles in various Lewis-acid promoted reactions with cyclopentadiene. The resulting highly functionalized cycloadducts are useful intermediates for the synthesis, particularly for the optically active synthesis of 6-5-5 tricyclic hexahydro-4H-3,5-methanofuro[2,3-b]pyranol (3) with five contiguous chiral centers. This stereochemically defined crown-like heterocyclic derivative is an important high affinity ligand for a variety of highly potent HIV-1 protease inhibitors. Among the various dienophiles and Lewis acid-mediated reactions surveyed, 3-(4-methoxybenzoyl)acryloyl oxazolidinone as the dienophile and diethylaluminum chloride as the Lewis-acid provided the desired endo product with excellent diastereoselectivity. The cycloaddition was carried out in multi-gram scale and the cycloadduct was efficiently converted to alcohol 3 with high enantiomeric purity. The optically active ligand was then transformed into potent HIV-1 protease inhibitor 2.