A Modified Mannich-Type Reaction Catalyzed by VO(acac)₂

Abstract

A facile VO(acac)(2)-catalyzed in situ generation of iminium ions from amine N-oxides and their participation in a modified Mannich-type reaction is described.

C1‐Substituted N‐Alkyl Tetrahydroisoquinoline Derivatives through V‐Catalyzed Oxidative Coupling

“…Hwang and Uang have shown that a series of commercially available amine N-oxides could be converted to the corresponding iminium ion by treatment with a simple vanadium catalyst. [8] We reasoned that this strategy could be extended to tertiary tetrahydroisoquinoline N-oxides formed in situ from the parent amine (Scheme 1 b). [9] To begin our study, N-benzyl THIQ 1 was chosen as an appropriate test substrate, as the benzyl group can be potentially removed and thus allows further functionalization of the amine.…”

Biosynthetically Inspired Syntheses of Secu′amamine A and Fluvirosaones A and B

“…To remedy this regioselectivity issue, we envisioned an activating agent for the Polonovski reaction that can also act as an internal base for the desired syn ‐selective elimination. To our delight, treating 22 with a stoichiometric amount of vanadyl acetylacetonate furnished the C2‐oxidized enamine 20 in 61 % yield as a major product. The formation of 20 connoted access to the C2‐iminium ion intermediate 29 through the vanadium‐mediated intramolecular syn elimination by a deprotonation at C2 of the intermediate 28 .…”

Arylglycine-derivative synthesis via oxidative sp3C–H functionalization of α-amino esters

“…Among these, the addition reaction of a carbon nucleophile to imines or iminium ions through Mannich-type reaction appears more useful (Scheme 1, reactions 1–3). However, these reactions need expensive arylboronic acids (Petasis reaction) [4–9] and suitable leaving groups [10–12] as well as a metal catalyst (Polonovsky reaction; this route requires the preparation of amine N -oxide in advance) [13–14]. …”