Highlighting the Rich Chemistry of the Allenone Moiety

Abstract

Conjugated and non-conjugated allenones appear as recurring motifs in organic synthesis, natural products and mechanistic investigations showing unique properties and applications. The ability of allenones to build cycles has provided a direct access to strained systems, medium-sized rings, arenes, heterocycles and complex polycycles. In addition, allenones have served as models in mechanistic investigations and catalysis. The critic compilation herein presented will provide an exhaustive overview of the synthetic possibilities allenones may offer, which certainly will inspire our community in their search of more efficient synthetic methodologies, preparation of biological and pharmaceutical targets, and improve our knowledge in theoretical organic chemistry. Great part of this review will discuss synthetic aspects, catalysis innovation and mechanistic insights of the chemical transformations implying the allenone motif. In addition, many examples on total synthesis and pharmacologically active compounds will be described. We hope that this overview will be attractive to the organic chemistry, synthetic chemistry, catalysis, theoretical chemistry, natural products and medicinal chemistry communities. 3.5. Synthesis of Spirocycles and Bridged Structures 3.6. Open-Chain Structures from Allenones 3.7. Allenones in Total Synthesis 4.

Challenging Task of Ni-Catalyzed Highly Regio-/Enantioselective Semihydrogenation of Racemic Tetrasubstituted Allenes via a Kinetic Resolution Process

“…The chemistry of allenes with the intriguing structural architecture of the orthogonal cumulative π-system has been an area of considerable interest over the past few decades. − Allenes work as important building blocks with versatile reactivity and have always been regarded as the hybrids of alkenes and alkynes, which have been engaged in various chemical reactions to access complicated skeletons. A number of efficient transformations of mono- and disubstituted allenes are well developed in modern organic synthesis; however, tri- and tetrasubstituted allenes working as substrates have not always been an easy endeavor and are less developed (Scheme a). , Among them, the carbometalation of allenes with organometallic M–Nu intermediates always resulted in the chemo- and regioselective generation of two disparate carbometalated intermediates M-alkenyl INT (sp 2 -M bond formation) or M-π-allyl INT (sp 3 -M bond formation; Scheme b). − These highly reactive intermediates went through a variety of synthetic transformations and always required rare and expensive noble-metal catalysts, including protonation, annulation, β-hydride elimination, and reductive elimination, providing structurally important organic molecules.…”

Photoredox-Catalyzed 1,4-Peroxidation–Sulfonylation of Enynones: A Three-Component Radical Coupling Approach for the Synthesis of Highly Functionalized Allenes

“…Given the widespread synthetic utility of cumulenes, the synthesis of functionalized allenes such as allenols and allenones has attracted considerable interest from the synthetic community. As one of the direct allenylation strategies, the transition metal-catalyzed addition reactions to 1,3-enynes provide the metalated allenyl intermediates that lead to the related allenyl products under thermodynamic control (Scheme a).…”

Regioselectivity Control in the Synthesis of Linear Conjugated Dienes Enabled by Manganese(I)-Catalyzed C–H Activation

“…Allenes, with two orthogonal CC double bonds, play an important role in transition-metal-catalyzed transformations thanks to the strong affinity of C–metal nucleophiles for π-bonds. However, in contrast to their alkyne and alkene analogues, allenes exhibit a more versatile reactivity, where the electronic and steric nature of the substituents can directly affect the insertion pattern of the organometallic species . Specifically, in metal-catalyzed C–H functionalization reactions, these cumulenic compounds can proceed mainly through either metal–allyl or metal–alkenyl intermediates, which makes the control of the selectivity a high challenge in allene-participated protocols (Scheme b) …”