Addition of Nitromethane to Aldoses. – A Comprehensive Study of the Diastereoselectivity of the Fischer‐Sowden Reaction by the Help of ^13^C‐NMR Spectroscopy^1)^
The addition of nitromethane to aldoses, commonly referred to as „Fischer‐Sowden reaction”︁, is not as stereoselective as can be concluded from the literature. This is the outcome of a comprehensive study which covered besides glyceraldehyde all aldotetroses, ‐pentoses and ‐hexoses. The ratio of the pair of diastereomeric nitroalditols has been determined in each case by ^13^C‐NMR spectroscopy. Thus, incidentially, a whole set of spectral data for all tetritols, pentitols, hexitols and heptitols with a terminal nitro group has been obtained, which can be correlated systematically to the respective data for the parent alditols. From these results follows that at least under conditions which give high yields of products, the reaction is thermodynamically controlled; thus, the product ratio is determined by the different energy content of the product nitroalditols (or their nitronates), which is a result of different patterns of steric interactions between substituents.