[3]Dendralensynthese: Rhodium(III)‐katalysierte Alkenyl‐C‐H‐ Aktivierung und Kupplungsreaktion mit Allenylcarbinolcarbonat

Abstract

Dendralene, auch bekannt als acyclische kreuzkonjugierte Polyene, wurden lange als wichtige Klasse mehrfach ungesättigter Kohlenwasserstoffe vernachlässigt. [1] Wegen ihrer einzigartigen Rolle in Polymerchemie, [2] theoretischer Chemie [3] und Synthesechemie [4] wuchs allerdings in den vergangenen Jahren das Interesse an Dendralenen. Dabei ist es wenig überraschend, dass die einfachsten Dendralene, [5] die [3]Dendralene oder kreuzkonjugierten Triene, am meisten Aufmerksamkeit erhalten haben. [2][3][4] Ihre Wichtigkeit spiegelt sich wider in ihrem Vorkommen als Motivstruktur in einer steigenden Zahl an Naturstoffen, [6] und besonders in ihrer Verwendung bei Dien-transmissiven Diels-Alder-Reaktionen (DTDA), [7] die eine rasche Konstruktion von komplexen mehrcyclischen Strukturen ermçglicht (Schema 1). [8]

Cross-Coupling Reactions between Alkenes by C–H Cyclometalation

“…A final β-oxygen elimination occurred to produce triene product 20 and the rhodium catalytic species is regenerated (Scheme 20 B). 21…”

Formal SN‐Type Reactions in Rhodium(III)‐Catalyzed CH Bond Activation

“…Following these pioneering studies, various applications of this catalyst in the synthesis of important structural motifs and heterocycles have been developed in the last years. [7] Moreover, the advantageous reactivity of an intermediate rhodacycle to undergo insertion or addition reactions with p-systems was further extended to reactions with enones, [8] allenes, [9] isocyanates, [10] carbonyl compounds or carbon monoxide (Scheme 1). [11] Besides the above mentioned "addition-type" reactions, and the recently reported dehydrogenative cross-couplings of benzene derivatives and/or heterocycles, [12] several RhCp*-catalyzed C À C and C À heteroA C H T U N G T R E N N U N G atom bond formation reactions have been explored that are formally equivalent to simple substitution reactions (Scheme 1).…”

Synthesis of Stereodefined Borylated Dendralenes through Copper‐Catalyzed Allylboration of Alkynes

“…[8] Theh igh value of dendralenes and the growing interest in their chemistry calls for efficient synthetic methods.S of ar, procedures for the synthesis of dendralenes mainly rely on Niand Pd-catalyzed cross-coupling of alkenylmetal reagents with (bis)haloalkenes. [2,9] Aside from these transformations, other elegant catalytic alternatives include Rh-catalyzed C À H-activation, [10] Pd-and Rh-catalyzed coupling of allenyl derivatives [11,12] and Ru-catalyzed cascade reactions. [13] However,all of these synthetic methods require the pre-formation of the starting materials,t hus adding extra steps.M oreover, strategies that allow the synthesis of functionalized dendralenes are scarce and most of them require building blocks with preinstalled functional groups.I nv iew of this and the enormous synthetic potential of dendralenes,i ti sd esirable to develop catalytic methods that allow rapid access to functionalized dendralenes from simple and commercially available materials.F urthermore,i nstallation of av ersatile functional group such as ab oronic ester in the dendralenic structure would result in an organoboron compound of tremendous synthetic use since awide variety of dendralenes could be accessed through CÀBb ond functionalization [14] (dendralene to dendralene conversion), and synthesis of complex polycyclic structures bearing the boronic ester group could be accomplished by use of the unique dendralene reactivity.N otably,t ot he best of our knowledge,b orylated [3]dendralenes (and higher homologues) have never been reported.…”