Unexpected stability of δ-lactones with axial substituents rather than equatorial ones. Conformational evaluation by molecular mechanics and molecular orbital calculations

✍ Scribed by Yoshiki Morimoto; Haruhisa Shirahama

• Book ID: 104207493
• Publisher: Elsevier Science
• Year: 1997
• Tongue: French
• Weight: 684 KB
• Volume: 53
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(96)01138-6

✦ Synopsis

A 1:1 mixture of the trisubstituted ~,-lactones 5a and 5b was subjected to thermodynamically equil~rated conditions to give predominantly 5b with axial subsfituents rather than 5a with all equatorial ones, in contrast to the Prelog-Djerassi lactone derivatives 3a and 3b. Further surprisingly, it has been found that the disubslltuted lactone 15 also adopts a haft-chair conformation with axial substituents. The conformational analyses of these compounds by molecular mechanics and molecular orbital calculations have emphasized gauche effects aad electrostatic interactions as a cause of the preference for axial conformers.