FeCl 3 Catalyzed Synthesis of cis ‐Fused Reduced THC Analogues

Studies on a cycloisomerization reaction of 2-prenylated-2Hpyrans towards cis-fused tetrahydro-6H-benzo[c]chromene systems (reduced cis-THC analogues) are reported. The transformation is catalyzed by iron chloride and proceeds with the formation of two new bonds and two stereocenters diastereoselectively. The same catalyst also promotes the formation of these products via a one-pot tandem Knoevenagel condensation of 1,3-cyclohexanediones and citral or farnesal aldehydes, followed by cycloisomerization establishing a direct assembly of this important scaffold.