[Zurück]

M. Draskovits, C. Stanetty, M.D. Mihovilovic:
"Diastereodivergence in the acyloxyallylation of protected and unprotected aldoses";
Poster: 18th Tetrahedron Symposium, Budapest; 27.06.2017 - 30.06.2017; in: "Abstract Book", (2017).

The indium mediated acyloxyallylation of aldoses, introduced by the Madsen group a decade ago is an elegant way for the two-carbon elongation of reducing sugars (upon ozonolysis). In this prove-of-concept study, the standard D-pentoses and D-hexoses were used as starting materials, giving rise to heptoses and octoses, respectively. Isolation of the main isomer showed that out of the four possible diastereomers, the product with lyxo-configuration (syn, anti- addition) is dominant in all cases investigated. Recently, we have developed this methodology into the first short synthesis of L-glycero-D-manno heptose at scale starting from L-lyxose. Within this study we also elucidated the two other diastereomers formed, thus identifying the type of selectivity observed when applied to reducing sugars. To expand on this, we set out to engage in an in-depth methodological investigation. We chose the L-tetroses as starting materials in order to obtain L-hexoses as products, for which authentic samples are available, allowing unambiguous identification. We found a comparable selectivity with L-erythrose and L-threose. Furthermore, a pronounced diasterodivergenz was found whether or not 2O,3O-protection was in place in the starting material. We evaluated the effect of steric bulk in the reagent on the diastereoselectivity in a systematic manner and could even achieve transformation with cheap zinc instead of indium. However, a complete loss of selectivity was observed, rendering this otherwise attractive modification useless. As a synthetically valuable side-line, we could establish a short scalable protocol towards L-allose, representing a second example of an exotic sugar made more readily available via acyloxyallylation.

Carbohydrates, Acyloxyallylation, Indium, Diastereodivergence

http://publik.tuwien.ac.at/files/publik_264357.pdf