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.
“…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.…”
Four-membered nitrogen-containing heterocycles are highly desirable functional groups with synthetic and biological applications. Unsaturated 4-membered N-heterocycles, 1- and 2-azetines, are historically underexplored, but have recently been gaining increased interest due to the development of new synthetic methods to access these compounds, and to their potential as reactive intermediates. This review covers new strategies for the synthesis of 1- and 2-azetines with a particular focus on advances made since 2018. Additionally, the use of these compounds as intermediates to access other heterocycles (3- to 6-membered) and complex products is comprehensively discussed.
“…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.…”
Four-membered nitrogen-containing heterocycles are highly desirable functional groups with synthetic and biological applications. Unsaturated 4-membered N-heterocycles, 1- and 2-azetines, are historically underexplored, but have recently been gaining increased interest due to the development of new synthetic methods to access these compounds, and to their potential as reactive intermediates. This review covers new strategies for the synthesis of 1- and 2-azetines with a particular focus on advances made since 2018. Additionally, the use of these compounds as intermediates to access other heterocycles (3- to 6-membered) and complex products is comprehensively discussed.
“…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).…”
Section: ■ Introductionmentioning
confidence: 99%
“…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 …”
Cycloaddition reactions offer great
advantages regarding atom and
step economy for the construction of various carbocycles and heterocycles.
While the recent development based on sensitized visible light photocatalysis
allowed the synthesis of azetidines via imine-alkene [2 + 2] cycloaddition,
imine-alkyne [2 + 2] cycloaddition under visible light photocatalysis
has not been reported. In this regard, we report the synthesis of
pyrrolizidinones based on intramolecular imine-alkyne [2 + 2] cycloaddition
under visible light photocatalysis. This redox-neutral reaction involves
formal imine-alkyne metathesis followed by redox-mediated annulation
with concomitant rearrangement. In contrast, the use of imino-alkenes
provides dihyro-1,4-oxazines via an alternative [4 + 2] cycloaddition
pathway. The proposed reaction mechanisms were supported by control
experiments and DFT calculations.
“…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.…”
The addition of nucleophilic organometallic species onto in situ generated azabicyclobutanes enables the selective formation of 3-arylated azetidine intermediates through strain-release. Single pot strategies were further developed for the N-arylation...
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