Uncommon Four‐Membered Building Blocks – Cyclobutenes, Azetines and Thietes

Abstract

Strained ring systems have gained considerable importance over the last few years for their implication in natural product syntheses or in drug discovery programs. We present herein a recollection of our work on the construction and functionalization of unsaturated four‐membered carbo‐ and heterocycles in the context of the literature, as well as their applications in further reactions.

New Strategies for the Synthesis of 1- and 2-Azetines and Their Applications as Value-Added Building Blocks

“…Previous reviews have focused on providing overviews of established methods to access 1-and 2azetines. [54][55][56] This comprehensive review will highlight advances made in the area of azetine synthesis since 2018.…”

Synthesis of Bicyclic N-Heterocycles via Photoredox Cycloaddition of Imino-Alkynes and Imino-Alkenes

“…Among the synthetic methods for these small size rings, it is notable that the synthesis of azetines is scarce with only a few methods reported. 7 Meanwhile, efforts based on visible light photocatalysis 8−10 led to the development of various four-membered ring syntheses. 11−13 For example, an energy transfer (EnT) mechanism has been exploited for the synthesis of cyclobutanes and cyclobutenes via alkene−alkene 14,15 and alkyne−alkene 16 cycloadditions, respectively (Figure 1A).…”

“…Cycloaddition is among the most efficient methods for the construction of new ring systems, which allows the formation of multiple bonds in a single step by joining independent π-systems with high diastereoselectivity and stereoselectivity. , Four-membered rings, including carbocycles and heterocycles, present unique challenges for synthesis owing to their high ring strains. , [2 + 2] cycloaddition has proven to be an efficient approach, for which ultraviolet (UV) irradiation and transition metal catalysis have been extensively studied. Among the synthetic methods for these small size rings, it is notable that the synthesis of azetines is scarce with only a few methods reported …”

Strain-release arylations for the bis-functionalization of azetidines

“…Despite efforts mentioned above, the introduction of aryl moieties at position 3 of aza-bicyclobutanes through strain-release remains undisclosed. With a general interest in 4-membered carbo- and heterocycles and their implication in drug discovery, 13 we set out to establish a reliable method for the construction of such functionalized azetidine architectures.…”