Rhodium(III)‐Catalyzed Synthesis of Skipped Enynes via C(sp³)–H Alkynylation of Terminal Alkenes

Abstract

The RhIII‐catalyzed allylic C−H alkynylation of non‐activated terminal alkenes leads selectively to linear 1,4‐enynes at room‐temperature. The catalytic system tolerates a wide range of functional groups without competing functionalization at other positions. Similarly, the vinylic C−H alkynylation of α,β‐ and β,γ‐ unsaturated amides gives conjugated Z‐1,3‐enynes and E‐enediynes.

Rhodium-catalysed ortho-alkynylation of nitroarenes

“…As part of our research program on the selective C–H alkynylation of functionalized molecules, we recently found that the combination of a Cp*Rh( iii ) catalyst and bromo-alkyne 2a is a highly active system for the alkynylation of a broad-range of C–H bonds. 12 Our initial attempts to extend this reactivity to 2-methylnitrobenzene ( 1a ) at 50 °C proved unsuccessful ( Table 1 , entry 1). Interestingly, formation of the corresponding alkynylated product 3a could be observed at 80 °C as the only product ( Table 1 , entry 2).…”

“…S13 † ). Both the Hammett and NBO analysis suggest that the Rh-catalysed C–H activation corresponds to an electrophilic concerted metalation deprotonation process, 12 in which both an electrophilic metal and a basic ligand cooperate in the cleavage of the C–H bond and subsequent rhodacycle formation.…”

Tetrasubstituted 1,3-Enynes by Gold-Catalyzed Direct C(sp2)–H Alkynylation of Acceptor-Substituted Enamines

“…Thus, it is not surprising that considerable efforts have been expended in seeking methods for the preparation of conjugated 1,3-enynes. Classical synthetic strategies for the construction of 1,3-enynes include Wittig olefinations of propynals or ynones, dehydrations of propargyl alcohols, cross-dimerizations of alkynes, and Sonogashira as well as Suzuki-Miyaura coupling reactions. , Over the past decade, the direct alkynylation of alkenes has gained more attention . Usually, the alkynylation of C­(sp 2 )–H bonds to give 1,3-enynes is limited to activated olefins or substrates bearing a proper directing group .…”

Reactivity of Stabilized Vinyldiazo Compounds toward Alkenyl- and Alkynylsilanes under Gold Catalysis: Regio- and Stereoselective Synthesis of Skipped Dienes and Enynes

“…These motifs are highly attractive because they are valuable building blocks and also structural motifs in natural products and biologically active compounds and new synthetic procedures for their synthesis would be highly desirable. 23 …”

“…Encouraged by the results obtained with vinylsilanes, we next wondered whether alkynylsilanes could serve as suitable coupling partners, thus providing a convenient access to skipped enynes. These motifs are highly attractive because they are valuable building blocks and also structural motifs in natural products and biologically active compounds and new synthetic procedures for their synthesis would be highly desirable …”