Enantioselective Total Synthesis of the Macrocyclic Spermidine Alkaloid (−)-Oncinotine

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.

Versatile Scope of a Masked Aldehyde Nitrone in 1,3-Dipolar Cycloadditions

A new masked aldehyde-containing nitrone 1 that is easily available through a facile one-step procedure has been developed. It undergoes a [3 + 2]-thermal cycloaddition with a wide range of dipolarophiles, affording isoxazolidine cycloadducts that are suitable for versatile postcycloaddition modifications. The acetal cycloadducts are acid-stable, but allow for acetal hydrolysis under mildly basic conditions. The isoxazolidine ring can be opened via an efficient one-pot procedure to give amine-protected γ-alcohols that can be further converted to furanose derivatives.

Asymmetric 1,3-dipolar cycloadditions of acrylamides

This critical review, which is relevant to researchers in synthetic organic chemistry, focuses on asymmetric 1,3-dipolar cycloadditions with acrylamides. The use of chiral acrylamides as dipolarophiles leads to high levels of stereocontrol, due to conformational constraint in the acrylamides. Employment of chiral tertiary acrylamides containing nitrogen heterocycles is particularly effective in controlling the stereoselectivity. Following a general overview of 1,3-dipolar cycloadditions, the main body of the review focuses on asymmetric 1,3-dipolar cycloadditions of acrylamides with nitrile oxides, nitrones, diazoalkanes and azomethine ylides, with particular emphasis on the rationale for the observed stereocontrol (215 references).

Asymmetric Total Synthesis of (+)-Cannabisativine

The asymmetric total synthesis of natural (+)-cannabisativine 1 was completed in 19 steps and 7% overall yield. The key synthetic intermediate 29 was prepared with a high degree of stereocontrol in 12 steps starting from chiral 1-acylpyridinium salt 10. Addition of zinc enolate 11 to pyridinium salt 10 furnished dihydropyridone 12 containing two contiguous stereocenters of the correct absolute configuration. Luche reduction of ketone 16 afforded diol 17 in high yield (96%) and excellent diastereoselectivity. The Mukaiyama-Michael reaction of pyridones 27a/b with O-silyl ketene acetal 32 gave phenyl selenyl ketones 33a/b with complete stereoselectivity. Elimination of cis-beta-hydroxyselenides 34 and 35 effected the regiocontrolled preparation of tetrahydropyridine derivative 29. Several approaches to the macrocyclic ring closure of the 13-membered ring were investigated, ultimately leading to the completion of an asymmetric synthesis of the target compound with a high degree of stereocontrol.

Catalysis-based enantioselective total synthesis of the macrocyclic spermidine alkaloid isooncinotine

A concise and efficient total synthesis of the spermidine alkaloid (-)-isooncinotine (1) incorporating a 22-membered lactam ring is outlined. The approach is largely catalysis-based, involving a selective iron-catalyzed alkyl-aryl cross-coupling reaction of a difunctionalized pyridine substrate, a heterogeneous asymmetric hydrogenation step to set the chiral center of the target, and a highly integrated ring-closing metathesis/hydrogenation sequence to forge the saturated macrocyclic edifice in a single operation.