Organocatalysis by bimacrocyclic NHCs: unexpected formation of a cyclic hemiacetal instead of a gamma-butyrolactone.

Ole Winkelmann, Christian Näther, Ulrich Lüning

Index: Org. Biomol. Chem. 7(3) , 553-6, (2009)

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Abstract

Two bimacrocyclic imidazolinium salts of different size, precursors to respective NHCs (N-heterocyclic carbenes), were tested as precatalysts in the reaction of aromatic aldehydes or ketones with enals. The expected lactones were produced in most cases, but in the reaction of methyl 4-formylbenzoate with cinnamaldehyde, the larger bimacrocycle led to the formation of a cyclic hemiacetal, while the smaller bimacrocycle gave the anticipated lactone.