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20.2.11.1.3.1 Variation 1: Knoevenagel–Doebner Condensation

DOI: 10.1055/sos-SD-020-00532

Vanderwal, C. D.; Jacobsen, E. N.Science of Synthesis, (200720558.

The classic Knoevenagel reaction of malonic esters with aldehydes to form alkylidene malonates has a variant named the Doebner condensation that utilizes malonic acid, generating the alk-2-enoic acid after in situ decarboxylation. This reaction is very general for aromatic and heteroaromatic aldehydes, as exemplified by the near quantitative conversion of highly functionalized benzaldehyde 33 into the corresponding unsaturated acid 34 (Scheme 9).[‌28‌] However, its application to aliphatic aldehydes is limited. One particularly successful example is the homologation of the bicyclic succinimidyl aldehyde 35 to the alk-2-enoic acid 36 in 75% yield.[‌29‌]

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