Rh(II)-Catalyzed Enynal Cycloisomerization for the Generation of Vinyl Carbene: Divergent Access to Polycyclic Heterocycles

Abstract

Described herein is an unprecedented example of generating the endocyclic donor–donor vinyl carbene achieved by the dirhodium­(II)-catalyzed enynal cycloisomerization. The endocyclic vinyl carbene intermediate could be trapped by a diversity of alkenes, including 1,1-disubstituted alkenes, dienes, and α-methyl styrenes, which could undergo [2 + 1], [4 + 3] cycloaddition and an unexpected formal allylation, respectively, giving spiro and fused polycyclic heterocycles. In these cascade transformations, up to three rings and three stereocenters were constructed in one step with good selectivities. The enantioselective versions were also achieved with up to 84% ee. Mechanistic studies revealed that a concerted intramolecular [2 + 3] cycloaddition was the key step for the generation of vinyl Rh­(II) carbene. Detailed studies were conducted to elucidate the intriguing mechanism of the formal allylation.

Superior Catalytic Performance and Methanol Tolerance of Co@Mesoporous Graphene Nanocomposites toward Oxygen Reduction Reaction

“…Figures 3d–f show the XPS spectrum of Co−Gs nanocomposites with Co, C and O in the composite nanomaterials. The Co 2p spectrum can be deconvoluted into peaks representing Co 0 (777.8/793.2 eV), Co 2+ (781.1/796.5 eV), and satellite peaks (786.3/802.5 eV), as shown in Figure 3d [35,36] . The high‐resolution C 1s spectrum of 0.1 M Co (Figure 3e) exhibits two independent peaks near 284.8 eV and 285.9 eV, corresponding to C−C, C−O functional groups.…”

“…The Co 2p spectrum can be deconvoluted into peaks representing Co 0 (777.8/793.2 eV), Co 2 + (781.1/796.5 eV), and satellite peaks (786.3/802.5 eV), as shown in Figure 3d. [35,36] The highresolution C 1s spectrum of 0.1 M Co (Figure 3e) exhibits two independent peaks near 284.8 eV and 285. 3g-i, respectively, confirming the uniform distribution of these elements in the composite material.…”

Dirhodium: carbene transformations and beyond

“…Moreover, detailed In 2022, they further demonstrated that the easily available benzo-enynal 19 could be catalyzed by dirhodium to generate the rare endocyclic donor-donor vinyl carbene 19-A (Scheme 7). 29 This sterically encumbered dirhodium carbene could be intercepted by a diverse range of alkenes, such as styrenes 20, dienes 22 and α-methyl styrenes 24, to give a collection of polycyclic heterocycles. Mechanistic studies revealed that the 1,1-disubstituted enynal was the prerequisite for the formation of the vinyl dirhodium carbene intermediate and the formal allylation products 25 originated from a combined C-H functionalization/Cope rearrangement 30 and subsequent 1,3-H shift which was confirmed by rigorous deuterium experiments.…”