Synthesis of 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic) derivatives by cycloaddition approaches

A new and general synthetic methodology for the preparation of functionalized 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid derivatives by a cycloaddition strategy is described. The synthesis of various enyne building blocks 12, 13, 21, and 22 containing an alpha -amino acid moiety using Schiff base 8 as a glycine equivalent has been achieved under mild reaction conditions. These building blocks have been utilized in the synthesis of inner-outer ring dienes 23 and 24 and exocyclic dienes 26 and 29, the key steps being an enyne metathesis reaction and cycloisomerization. Various topographically constrained Tic derivatives have been synthesized using dienes containing an alpha -amino acid moiety through Diels-Alder reactions. For the first time, [2+2+2] cyclotrimerization, as promoted by Wilkinson's and Vollhardt's catalysts, has been used for the synthesis of various highly functionalized Tic derivatives.