roflamycoin

Synthesis

For Rychnovsky and co-worker’s synthesis of roflamycoin (45), the hemiketal-pyran linkage required differential substitution (Scheme 9) and demonstrated the power of the sequential double addition strategy.14 Treatment of bis-epoxide S,S-4 with a stoichiometric amount of (benzyloxy)methyllithium 38 and BF3?OEt2 in THF at –78 °C provided monoaddition adduct 39, which was then treated with the organolithium formed from transmetallation of 2,2-bis-(tributyltin)dithiane 40. This single-pot procedure afforded dithiane diol 41 in 56% overall yield. Subsequent acetonide formation and transmetallation provided a competent nucleophile for direct displacement of dibromide 42, which itself was derived from dichlorodiol R,R-3. The resulting bis-acetonide (43) was obtained in 60% overall yield and provided a rapid access to tris-acetonide 44, a key intermediate for the synthesis of the hemiketal-pyran moiety of 45. Similar sequential addition strategies have proven to be useful as well.