High-Yield Synthesis of 20-, 24-, and 28-Membered Macropentolide, -hexolide,and -heptolide,Respectively, from (R)- or (S)-3-hydroxybutanoic acid under Yamaguchi's macrolactonization conditions

The macrocyclic pentolide 1 , hexolide 2 , and heptolide 3 constitute ca. 80% of the oligomers formed in ca. 50% yield from enantiomerically pure 3-hydroxybutanoic acid under Yamaguchi's macrolactonization conditions. The FAB mass spectra of the MH⁺, M Na⁺, and MCs⁺ are reported (Figs. 2, 3, 5, and 6). No cyclic tetramer is detected. The ¹H-NMR spectra of the cyclic oligomers, of the monomer, and of the polymer (PHB) are very similar (Fig. 4). Directed synthesis of the open-chain dimer and tetramer of 3-hydroxybutanoic acid and attempted cyclization do not lead to the isolation of the cyclic tetramer.