Abstract
The development of an N-heterocyclic carbene (NHC) catalysed intercepted dehomologation of aldoses is reported. The unique selectivity of NHCs for aldehydes is exploited in the complex context of reducing sugars. Examples of strong substrate governance for either intercepted dehomologation or a subsequent redox-lactonisation were identified and mechanistically understood. More importantly, it was shown that catalyst design allowed the tuning of the selectivity of the reaction with structurally unbiased starting materials towards either of the two scenarios.
Highlights
ISSN 1359-7345 COMMUNICATION Jong Seung Kim, Kitae Kim et al Enhanced sensitivity of fluorescence-based Fe(II) detection by freezing
The unique selectivity of N-heterocyclic carbene (NHC) for aldehydes is exploited in the complex context of reducing sugars
It was shown that catalyst design allowed the tuning of the selectivity of the reaction with structurally unbiased starting materials towards either of the two scenarios
Summary
Dehomologation towards shortened carbohydrates (e.g. by the Wohl degradation) initiate by addressing the aldehyde moiety.[7] Requirements of stoichiometric amounts of reagents and/or limited compatibility with unprotected aldoses due to solubility and cross-reactivity with the free hydroxyl groups are major challenges in this field.[8] In this light, we perceived great potential for transformations triggered by the highly aldehyde-specific interaction of N-heterocyclic carbenes (NHCs) with the (anomeric) carbonyl moiety which we have just started to exploit. The thereby achieved formylation of a,b-unsaturated compounds in a subsequent Stetter reaction was the goal of the study, with the sugars being utilised as a sacrificial feedstock.[18] Inspired by these works and building upon the proposed mechanism, we set out to develop an NHC controlled intercepted dehomologation methodology of carbohydrate derivatives. The influence of solvent, type of base as well as lower and higher temperatures has been evaluated which is summarized for 1b as a starting material in
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