α-Ketol and α-iminol rearrangements in synthetic organic and biosynthetic reactions

Abstract

In the presence of a suitable acid or base, α-hydroxyaldehydes, ketones, and imines can undergo isomerization that features the 1,2-shift of an alkyl or aryl group. In the process, the hydroxy group is converted to a carbonyl and the aldehyde/ketone or imine is converted to an alcohol or amine. Such α-ketol/α-iminol rearrangements are used in a wide variety of synthetic applications including asymmetric synthesis, tandem reactions, and the total synthesis and biosynthesis of natural products. This review explores the use of α-ketol rearrangements in these contexts over the past two decades.

Switchable Skeletal Rearrangement of Hexahydro-4H-indol-4-ones: Divergent Synthesis of Dihydroxy-4H-cyclopenta[b]pyridin-4-ones and 8-Alkenyl Oxepane-2,6-diones

“…To elucidate the process of this base-controlled selective controllable skeletal rearrangement transformation of hexahydro-4 H -indol-4-ones, a possible mechanism has been proposed based on some previous literature. , As shown in Scheme , the deprotonation of 1a initiated in the presence of LiOH to give A , and then, the lithium ion was complexed with the two carbonyl groups in the structure to form the intermediate B , which underwent an α-ketol rearrangement to give the desired product 2a (path a). The initiation process for the formation of 8-alkenyl oxepane-2,6-dione 3a is shown in path b.…”

1,2-Redox Transpositions of Tertiary Amides

“…Taking inspiration from the Amadori and α-iminol rearrangements (35,36), we believed that appropriate β-oxidation of the enamine to the hydroxy-iminium ion should then follow a related mechanistic course and tautomerize to the thermodynamically more stable α-aminoketone. Indeed, enamine oxidation has been demonstrated on "N-deactivated" substrate classes, e.g.…”