[Stereoselective Synthesis of Multi-substituted Fluoro-β-lactams and Their Conversion to Fluorinated β-Amino Acid Core]

Multi-substituted β-lactam compounds have not only attracted considerable interest as core structures of pharmaceutical compounds such as antibiotics but also have been used as building blocks for the construction of β-amino acids. Electrophilic β-lactams can be used to enhance essential biological activities. Furthermore, the ring-opening reactions of electrophilic β-lactams can be used to provide facile access to β-amino acids. The introduction of an electronegative fluorine atom to a β-lactam ring to give the corresponding fluoro-β-lactam can be used as an effective strategy for the preparation of electrophilic β-lactams. In this review, we provide a summary of our recent research towards the direct functionalization of fluoro-β-lactams. This review has been divided into four topics, including: 1) the alkylation and hydroxyalkylation of α-bromo-α-fluoro-β-lactams (1); 2) the nickel-catalyzed cross coupling reaction of 1; 3) the asymmetric synthesis of fluoro-β-lactams using chiral ligands; and 4) the utilization of fluoro-β-lactams as highly electrophilic building blocks.

Diastereoselective Synthesis of syn-β-Lactams Using Rh-Catalyzed Reductive Mannich-Type Reaction of α,β-Unsaturated Esters

The combination of Et2Zn and RhCl(PPh3)3 led to the facile generation of a rhodium-hydride complex (Rh-H) that catalyzed the 1,4-reduction of α,β-unsaturated esters. The resulting rhodium enolate performed as a Reformatsky-type reagent and reacted with various imines to give syn-β-lactams in good to excellent yields with high diastereoselectivity.

Synthesis of a fluorinated Ezetimibe analogue using radical allylation of α-bromo-α-fluoro-β-lactam

A facile and efficient synthesis of a fluorinated Ezetimibe analogue was achieved by radical allylation, Wacker oxidation, and nucleophilic arylation of α-bromo-α-fluoro-β-lactam.

One-pot synthesis of 1,3-enynes with a CF3 group on the terminal sp2 carbon by an oxidative Sonogashira cross-coupling reaction

One-pot synthesis of 1,3-enynes with a CF₃ group on the terminal sp² carbon was achieved by an oxidative Sonogashira cross-coupling reaction with (E)-trimethyl(3,3,3-trifluoroprop-1-enyl)silane.

Csp3-csp3 homocoupling reaction of benzyl halides catalyzed by rhodium

A highly reactive alkylrhodium complex was formed from Me(2)Zn and RhCl(PPh(3))(3) and effectively catalyzed a Csp(3)-Csp(3) homocoupling reaction of benzyl halides. A Csp(3)-Csp(3) coupling reaction using Rh catalyst has not been reported up to now. The reaction proceeded under very mild conditions and gave the corresponding homocoupling products even if they had reactive substituents such as an uncovered formyl or hydroxymethyl group.

Enantioselective synthesis of α,α-difluoro-β-lactams using amino alcohol ligands

A practical and highly enantioselective Reformatsky reaction of ethyl bromodifluoroacetate with imines using a cheap and commercially available amino alcohol ligand is described.

Oxidative 3,3,3-trifluoropropylation of arylaldehydes

A reaction between (E)-trimethyl(3,3,3-trifluoroprop-1-en-1-yl)silane (1) and arylaldehydes 2 was triggered by fluoride anions to afford aryl 3,3,3-trifluoropropyl ketones 3 in moderate to good yield. A mechanistic study of this reaction indicated that it occurred via an allyl alkoxide (4). A subsequent 1,3-proton shift of the benzylic proton of 4 forms 3. This reaction involves oxidative 3,3,3-trifluoropropylation of an arylaldehyde to afford 4,4,4-trifluoro-1-arylbutan-1-one.

Direct and diastereoselective alkylation and aldol reactions of α-bromo-α-fluoro-β-lactams

Herein, we describe the development of a method for the direct alkylation and aldol reaction of α-bromo-α-fluoro-β-lactams. This method provides facile access to a wide range of 3-alkyl- and 3-hydroxyalkyl-fluoro-β-lactams in good yields under mild conditions. The products were obtained with complete diastereoselectivity with regard to the relative configuration of the β-lactam ring at C3 and C4 positions. The reaction conditions were tolerant of a broad range of electrophiles, which highlights the overall scope and utility of this procedure.