Simple synthesis of (S)-parasorbic acid and other (5S)-hydroxy six-carbon synthons from L-rhamnose

The scientific legacy of Frieder W. Lichtenthaler

This article presents a selection of topics from Professor Frieder W. Lichtenthaler's scientific lifework. It describes his contributions to, and further development of, the nitromethane cyclization of dialdehydes leading to amino sugars and amino nucleosides, as well as a new coupling methodology for purine nucleosides. A number of chiral building blocks derived from sugars like the "sugar enolones," enollactones, hydroxyhexenals, and their synthetic applications in natural product syntheses are covered. The article further describes the chemistry of "ulosyl bromides" and their glycosidation reactions, including those with bifunctional acceptors, which led to the synthesis of spectinomycin and gomphoside. Lichtenthaler's work on the preparation of synthetically useful building blocks from disaccharides that are readily available in bulk quantities, and his studies on the reactivity, as well as the selective O-functionalization of sucrose, higher oligosaccharides, and cyclodextrins based on computer simulations, are highlighted. The article also presents his research on the syntheses of chiral building blocks from readily available ketoses and their synthetic applications. Finally the chapter concludes with his significant contributions in the field of the history of carbohydrate chemistry.

Proline-catalyzed one-step asymmetric synthesis of 5-hydroxy-(2E)-hexenal from acetaldehyde

For the first time, the L-proline-catalyzed direct asymmetric self-aldolization of acetaldehyde is described affording (+)-(5S)-hydroxy-(2E)-hexenal 2 with ee's ranging from 57 to 90%. Further transformations of 2 into synthetically valuable building blocks are presented. A mechanism for the formation of 2 is proposed.