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

Abstract 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 M H + , M Na + , and M Cs + are reported ( Figs. 2, 3, 5, and 6 ). No cyclic tetramer is detected. The 1 H‐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.