A stereoselective synthesis of a spiro-bridged bis(α-amino acid) derivative based on Ru(II)-catalysed RCM reactions

Methodology for a stereoselective synthesis of a member of a novel family of spiro-bridged bis(α-amino acid) derivatives is described. The key step in the construction is a spirane annulation reaction effected by a Ru(II)-catalysed ring-closing metathesis (RCM) reaction of an appropriately substituted tetraene. The latter became available after stereocontrolled allylations of 3,3-bis[2-((2S,5R)-5-isopropyl-3,6-dimethoxy-2,5-dihydropyrazin-2-yl)ethyl]-1,4-pentadiene, which was prepared in several reaction steps from (2R)-2,5-dihydro-2-isopropyl-3,6-dimethoxypyrazine as a chiral starting material.