Stereocontrolled construction of A.B.C.[6.6.6] tricycle via transannular Diels–Alder reaction of 14-membered macrocycle with acetylene as dienophile

Abstract

The syntheses of the acyclic dienynes 14a (cis-trans-acetylene) and 14b (trans-trans-acetylene) are described. The tandem macrocyclization and transannular Diels–Alder reaction of the allylic chloride 14b was conducted in the presence of Cs2CO3 at 85 °C in one-pot to provide tricyclic product 16, with the two hydrogens in ring B being cis. On the other hand, treatment of the allylic chloride 14a under the same conditions afforded 14-membered macrocycle 17, which could be transformed at 250 °C into a similar tricyclic product 18 with the two hydrogens in ring B being trans, along with an interesting by-product 19. The mechanism for the formation of 19 is also discussed. Keywords: stereocontrolled synthesis, macrocycle, tricyclic compound, transannular Diels–Alder reaction.