Efficient, asymmetric synthesis of (−)-isooncinotine

Recent applications of the Wittig reaction in alkaloid synthesis

The Wittig reaction is the chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide (the Wittig reagent) to afford an alkene and triphenylphosphine oxide. Noteworthy, this reaction results in the synthesis of alkenes in a selective and predictable fashion. Thus, it became as one of the keystone of synthetic organic chemistry, especially in the total synthesis of natural products, where the selectivity of a reaction is paramount of importance. A literature survey disclosed the existence of vast numbers of related reports and comprehensive reviews on the applications of this important name reaction in the total synthesis of natural products. However, the aim of this chapter is to underscore, the applications of the Wittig reaction in the total synthesis of one the most important and prevalent classes of natural products, the alkaloids, especially those showing important and diverse biological activities.

Enzymatic Kinetic Resolution of 2-Piperidineethanol for the Enantioselective Targeted and Diversity Oriented Synthesis

2-Piperidineethanol (1) and its corresponding N-protected aldehyde (2) were used for the synthesis of several natural and synthetic compounds. The existence of a stereocenter at position 2 of the piperidine skeleton and the presence of an easily-functionalized group, such as the alcohol, set 1 as a valuable starting material for enantioselective synthesis. Herein, are presented both synthetic and enzymatic methods for the resolution of the racemic 1, as well as an overview of synthesized natural products starting from the enantiopure 1.

Asymmetric synthesis of (+)-vertine and (+)-lythrine

The total syntheses of the Lythracea alkaloids (+)-vertine and (+)-lythrine are described. Enantioenriched pelletierine is used as a chiral building block and engaged into a two step pelletierine condensation leading to two quinolizidin-2-one diastereomers in a 8 : 1 ratio. The major product is used in the synthesis of (+)-vertine via aryl-aryl coupling and ring closing metathesis to provide a Z-alkene α to the lactone carbonyl function. The same procedure was used for (+)-lythrine after base induced epimerization of the main quinolizidin-2-one diastereomer. Alternative classical ring closure strategies like macrolactonisation or aryl-aryl coupling failed.

Straightforward access to enantioenriched 2-allylpiperidine: application to the synthesis of alkaloids

An efficient stereocontrolled preparation of (2R,R(S))-2-allyl-(N-tert-butylsulfinyl)piperidine and its enantiomer is detailed. The sequence requires only two synthetic operations with one-column chromatography and is readily scaled up. The versatility of these chiral building blocks was exemplified by the total or formal synthesis of some natural and unnatural alkaloids.