Practical synthesis of C1 deuterated aldehydes enabled by NHC catalysis

The recent surge in applications of deuterated pharmaceutical agents has created an urgent demand for synthetic methods that efficiently generate deuterated building blocks. Here, we show that N-heterocyclic carbenes promote a reversible hydrogen–deuterium exchange reaction with simple aldehydes, which leads to a practical approach to synthetically valuable C1 deuterated aldehydes. The reactivity of the well-established N-heterocyclic carbene-catalysed formation of Breslow intermediates from aldehydes is reengineered to overcome the overwhelmingly kinetically favourable benzoin condensation reaction and achieve the critical reversibility to drive the formation of desired deuterated products when an excess of D2O is employed. Notably, this operationally simple and cost-effective protocol serves as a general and truly practical approach to all types of 1-D-aldehydes including aryl, alkyl and alkenyl aldehydes, and enables chemoselective late-stage deuterium incorporation into complex, native therapeutic agents and natural products with uniformly high levels (>95%) of deuterium incorporation for a total of 104 tested substrates. Deuterated molecules are important both as labelled probes and as targets in their own right. Here the authors report a very simple and general deuteration of aldehydes, by the use of an N-heterocyclic carbene catalyst in the presence of D2O.