The Indium-mediated Acyloxyallylation – A Tool for the Elongation of Aldoses towards Non-natural Sugar Alcohols

Abstract

The synthesis of higher-carbon sugars and derivatives has been a challenge over decades. However, with the indium-mediated acyloxyallylation (IMA) a method was developed and investigated in the last years, that allows the direct elongation of unprotected aldoses by three carbons with high control of diastereoselectivity.[1,2] With the IMA as a tool in hand, our interest in the synthesis of sugar alcohols with more than six carbon atoms was raised by a computational study [3]. In this study, non-natural sugar alcohols were investigated as potential phase change materials (PCM) for thermal energy storage applications. The authors predicted extraordinarily high thermal storage densities of up to 450-500 kJ/kg for sugar alcohols that fulfil three structural criteria: a linear carbon backbone, an even number of carbon atoms and 1,3-anti configuration of all hydroxyl groups. In order to confirm these values and find further promising PCM candidates, we developed an efficient strategy for the synthesis of non-natural sugar alcohols that fulfil the stated rules. Some of the investigated sugar alcohols with manno-configuration presented in the computational study [3] were accessible via IMA and the calculated values could be confirmed with experimental data. Since the natural occurring galactitol has a higher latent heat of fusion than D-mannitol, our focus was on the synthesis of higher sugar alcohols with a syn-relationship between the two hydroxyl groups at the terminal stereocenters and a 1,3-anti-relationship of all hydroxyl groups, which we refer to as the "galacto-series".

[1] Palmelund A., Madsen.R., Eur. J. Org. Chem., 2005, 70(20), 8248-8251. [2] Draskovits M.; Stanetty C., Baxendale I.R., Mihovilovic M.D., J. Org. Chem., 2018, 83(5), 2647-2659. [3] Inagaki T.; Ishida T., J. Am. Chem. Soc., 2016, 138, 11810-11819.