Transannular Diels–Alder reactions on 14-membered macrocyclic trienes. Part I: stereoselective syntheses of the macrocyclic trienes precursors

Transannular Diels–Alder reactions on 14-membered macrocycles containing properly located diene and methyl-substituted dienophile units lead to A.B.C.[6.6.6] tricycles related to steroids. To study the influence of the olefin and diene geometry on the stereochemical outcome of the Diels–Alder reaction it was necessary to prepare macrocyclic trienes of well-defined stereochemistry. Eight different types of macrocyclic trienes might be obtained by the coupling of appropriate dienophiles and dienes, namely, TTC, TTT, TCC, TCT, CTC, CTT, CCC, and CCT. In this paper (first in a series of two), the synthesis of appropriately functionalized dienophile and diene synthons, as well as their coupling reaction affording macrocyclic triene precursors, is described.