Highly Diastereoselective Mannich-Type Reactions of Chiral N-Acylhydrazones

Rh-Catalyzed reductive Mannich-type reaction and its application towards the synthesis of (±)-ezetimibe

An effective synthesis for syn-β-lactams was achieved using a Rh-catalyzed reductive Mannich-type reaction. A rhodium–hydride complex (Rh–H) derived from diethylzinc (Et₂Zn) and a Rh catalyst was used for the 1,4-reduction of an α,β-unsaturated ester to give a Reformatsky-type reagent, which in turn, reacted with an imine to give the syn-β-lactam. Additionally, the reaction was applied to the synthesis of (±)-ezetimibe, a potent β-lactamic cholesterol absorption inhibitor.

One-pot three-component Mannich reaction in water catalyzed by eco-friendly, hydrophobic and recyclable sulfonic acid based nanosilica (SBA-15-Ph-PrSO3H)

A mild, effective and green method for the Mannich reaction of aromatic aldehydes, aromatic amines and ketones has been accomplished in good to excellent yields using hydrophobic SBA-15-Ph-PrSO₃H in water at room temperature.

Asymmetric synthesis of aminochromanes via intramolecular indium-mediated allylation of chiral hydrazones

The asymmetric intramolecular indium-mediated cyclization reaction delivers chromanes with excellent diastereoselectivity (68-91% yield, dr >99:1). The reaction was efficient for aryl substrates with both electron-withdrawing and -donating groups. Carboxylic acid additives were found to be necessary for optimal reaction.

One-pot three-component Mannich-type reactions using sulfamic acid catalyst under ultrasound irradiation

Sulfamic acid (NH(2)SO(3)H, SA) was used as an efficient, inexpensive, non-toxic and recyclable green catalyst for the ultrasound-assisted one-pot Mannich reaction of aldehydes with ketones and amines. This ultrasound protocol has advantages of high yield, mild condition, no environmental pollution, and simple work-up procedures. Most importantly, beta-aminocarbonyl compounds with ortho-substituted aromatic amines are obtained in acceptable to good yields by this methodology for the first time.

Enantiodivergent Synthesis of d- and l-erythro-Sphingosines through Mannich-Type Reactions of N-Benzyl-2,3-O-isopropylidene-d-glyceraldehyde Nitrone

The addition of a 2-silyloxy silylketene acetal to N-benzyl-2,3-O-isopropylidene-D-glyceraldehyde nitrone (Mannich-type reaction) can be stereocontrolled to give 2S,3S,4S and 2R,3R,4S adducts as major compounds, depending on whether the reaction is activated with zinc(II) triflate or tin(IV) chloride, respectively. The corresponding major adducts were used for preparing diastereomeric polyhydroxy-beta-aminoesters that were further converted into suitable orthogonally protected enantiomeric D- and L-erythro-sphingosines.

N-Acylhydrazones as Versatile Electrophiles for the Synthesis of Nitrogen-Containing Compounds

The use of N-acylhydrazones as electrophiles in reactions with nucleophiles has recently made some important advances. N-Acylhydrazones, which can be readily prepared and stored, act as stable imine surrogates in these reactions. The hydrazide products are useful, often chiral building blocks which can be transformed into various nitrogen-containing compounds by cleavage of the N--N bond. The N-acyl groups often play important roles as templates for metal catalysis in controlling stereochemistry. This Minireview summarizes the most recent results of N-acylhydrazone chemistry, and provides an overview of current developments in this field.

Succinct Synthesis of β-Amino Acids via Chiral Isoxazolines

beta-Amino acids are important synthetic targets due to their presence in a wide variety of natural products, pharmaceutical agents, and mimics of protein structural motifs. While beta-amino acids containing geminal substitution patterns have enormous potential for application in these contexts, synthetic challenges to the stereoselective preparation of this class of compound have thus far limited more complete studies. We present here a straightforward method employing chiral isoxazolines as key intermediates to access five different beta-amino acid structural types with excellent selectivity. Of particular note is the use of this approach to prepare highly substituted cis-beta-proline analogues. The ready access to these diversely substituted compounds is expected to facilitate future studies of the structure and function of this important class of molecules.

Synthesis of Enantiopure Sulfinimines (Thiooxime S-Oxides) Catalyzed by Yb(OTf)3 from p-Toluenesulfinamide and Aldehydes in Mild Reaction Conditions

Enantiomerically pure sulfinimines as important building blocks in the asymmetric synthesis of amine derivatives are prepared in good to excellent yields from chiral p-toluenesulfinamide with aromatic, heteroaromatic, and aliphatic aldehydes. The unprecedented feature of the reported procedure is that the formation of the sulfinimines was achieved by the catalytic action of Yb(OTf)(3) in THF at room temperature. The reaction conditions were also applicable to Ellman's sulfinimines.