Selective C-N σ Bond Cleavage in Azetidinyl Amides under Transition Metal-Free Conditions

Photocatalytic Carboxylation of C-N Bonds in Cyclic Amines with CO2 by Consecutive Visible-Light-Induced Electron Transfer

Visible-light photocatalytic carboxylation with CO₂ is highly important. However, it still remains challenging for reluctant substrates with low reduction potentials. Herein, we report a novel photocatalytic carboxylation of C-N bonds in cyclic amines with CO₂ via consecutive photo-induced electron transfer (ConPET). It is also the first photocatalytic reductive ring-opening reaction of azetidines, pyrrolidines and piperidines. This strategy is practical to transform a variety of easily available cyclic amines to valuable β-, γ-, δ- and ϵ-amino acids in moderate-to-excellent yields. Moreover, the method also features mild and transition-metal-free conditions, high selectivity, good functional-group tolerance, facile scalability and product derivations. Mechanistic studies indicate that the ConPET might be the key to generating highly reactive photocatalysts, which enable the reductive activation of cyclic amines to generate carbon radicals and carbanions as the key intermediates.

Recent advances in the synthesis and reactivity of azetidines: strain-driven character of the four-membered heterocycle

Azetidines represent one of the most important four-membered heterocycles used in organic synthesis and medicinal chemistry. The reactivity of azetidines is driven by a considerable ring strain, while at the same the ring is significantly more stable than that of related aziridines, which translates into both facile handling and unique reactivity that can be triggered under appropriate reaction conditions. Recently, remarkable advances in the chemistry and reactivity of azetidines have been reported. In this review, we provide an overview of the synthesis, reactivity and application of azetidines that have been published in the last years with a focus on the most recent advances, trends and future directions. The review is organized by the methods of synthesis of azetidines and the reaction type used for functionalization of azetidines. Finally, recent examples of using azetidines as motifs in drug discovery, polymerization and chiral templates are discussed.

Recent Advances in the Use of Sodium Dispersion for Organic Synthesis

This short review describes the recent emergence of organosodium chemistry, motivated by the requirements of modern synthetic chemistry for sustainability, and powered by the use of sodium dispersion, a form of sodium that is commercially available, easy to handle, and has a large active surface area. We present recent methods for the preparation of organosodium compounds using sodium dispersion, and their applications to synthesis. Sodium amides and phosphides are also briefly discussed.

1 Introduction

2 Sodium Dispersion

3 Preparation of Organosodium Compounds

3.1 Two-Electron Reduction of Aryl Halides

3.2 Halogen–Sodium Exchange

3.3 Directed Metalation

3.4 Cleavage of C–C and C–Heteroatom Bonds

4 Synthetic Applications

4.1 Reduction in Combination with a Proton Source

4.1.1 Bouveault–Blanc Reduction

4.1.2 Birch Reduction

4.1.3 Reductive Deuteration

4.1.4 Chemoselective Cleavage of Amides and Nitriles

4.2 Difunctionalization of Alkenes and Alkynes

5 Sodium Amides and Phosphides

6 Conclusions and Outlook

Synthesis of α-Deuterated Primary Amines via Reductive Deuteration of Oximes Using D2O as a Deuterium Source

Selective introduction of the deuterium atom into the α-position of amines is important for the development of all types of novel deuterated drugs and agrochemicals due to the pervasive presence of amines. In this study, we report the first general single-electron-transfer reductive deuteration of both ketoximes and aldoximes using SmI₂ as an electron donor and D₂O as a deuterium source for the synthesis of α-deuterated primary amines with excellent levels of deuterium incorporations (>95% [D]). This protocol exhibits excellent chemoselectivity and tolerates a variety of functional groups. The potential application of this new method was showcased in the synthesis of deuterated drugs, such as rimantadine-d₄, the tebufenpyrad analogue, derivatives of nabumetone and pregnenolone, and a series of building blocks for the rapid and general assembly of deuterated drugs and pesticides.

Reductive Cleavage of Unactivated Carbon-Cyano Bonds under Ammonia-Free Birch Conditions

A general protocol for the reductive cleavage of unactivated carbon-cyano bonds in aliphatic nitriles has been achieved under single-electron-transfer conditions using Na/15-crown-5/H₂O. Electron is supplied by the electride derived from bench-stable sodium dispersions and recoverable 15-crown-5. H₂O provides the proton source and suppresses the reduction of aromatic moieties. Compared with the Na/NH₃ electride system generated under traditional Birch conditions, this ammonia-free electride system is more practical and features better reactivity and chemoselectivity for the decyanations of a broad range of aliphatic nitriles.