Highly diastereoselective hydrogenations leading to ß-hydroxy ∂-lactones in hydroxy-protected form. A modified view of ∂-lactone conformations.

Summary, in English

Enol MEM ethers 4 and 15 and the corresponding enol acetates were hydrogenated over Pd/C with very high (>99%) diastereoselectivity to saturated -lactones. A stereochemical generalization can be formulated thus: trans-5,6-disubstituted 1-oxa-3-cyclohexen-2-ones (e.g. 14 and 15) are hydrogenated over Pd with high selectivity from the side trans to the C(6)-substituent. A mechanistic rationalization of the stereochemical outcome in the Pd-catalyzed hydrogenation of this as well as other types of substituted ,-unsaturated -lactones is presented. An analysis of X-ray crystallographic data for 67 compounds demonstrated a great conformational diversity of the saturated -lactone ring. Besides, ab initio calculations (HF/6-31G*) indicated a very high conformational mobility. Thus, the lowest calculated transition state for the conversion of the half-chair, most stable, conformer of -valerolactone to the boat-type conformer lies only 1.93 kcal/mol above the former. Beside these two conformers, also chair, envelope and skew conformations are accessible; all lie less than 2 kcal/mol above the half-chair. The previous conformational paradigm comprising only boat and half-chair types is incomplete

• Author: S Brandänge; M Färnbäck; H Leijonmarck; Anders Sundin
• Department/s: Centre for Analysis and Synthesis
• Publishing year: 2003
• Language: English
• Pages: 11942-11955
• Publication/Series: Journal of the American Chemical Society
• Volume: 125
• Issue: 39
• Links: http://dx.doi.org/10.1021/ja036002b
• Document type: Journal article review
• Publisher: The American Chemical Society (ACS)
• Topic: Organic Chemistry
• Status: Published
• ISBN/ISSN/Other: ISSN: 1520-5126