Formal Total Synthesis of Ipomeamarone via the [2+3] Dihydrofuran Annulation

A formal synthesis of (2R-cis)-4-methyl-1-(2,3,4,5-tetrahydro-5-methyl-2,3′-bifuran]-2-pentanone, or ipomeamarone (1) 494-23-5] was accomplished from 3-furaldehyde 5 and ethyl-2-bromocrotonate 4. The key step involved the formation of the dihydrofuran ring in 2 via a vinyloxirane rearrangement of 3 in the 2+3] dihydrofuran annulation. Mechanistic duality of reactions of those tetrahydrofurans possessing acidic hydrogens adjacent to the ring is addressed.