[2+2+1] Cyclization of allenes

Kitagaki, Shinji; Inagaki, Fuyuhiko; Mukai, Chisato

doi:10.1039/c3cs60382b

Cited by 126 publications

(41 citation statements)

References 91 publications

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“…[1][2][3] This chemical transformation, usually termed as the Pauson-Khand reaction (PKR), has gained attention within the field of organic chemistry since many natural products can be synthesized from it. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Besides cobalt, also other transition metals perform well in the PKR such as rhodium, [19][20][21] ruthenium, 22,23 palladium, 24 iridium, 25,26 iron, 27,28 tungsten, 29 molybdenum, 30,31 and chromium. 32,33 The PKR depends upon steric and electronic factors.…”

Section: Introductionmentioning

confidence: 99%

Regioselectivity of the Pauson–Khand reaction in single-walled carbon nanotubes

et al. 2018

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Chemical functionalization of nanotubes, in which their properties can be combined with those of other classes of materials, is fundamental to improve the physicochemical properties of nanotubes for potential technological applications. In this work, we theoretically and experimentally examine the Pauson-Khand reaction (PKR) on zig-zag, armchair, and chiral single-walled carbon nanotubes (SWCNTs). Our benchmarked density functional theory (DFT) calculations show that an alternative pathway to the widely accepted Magnus reaction pathway has significantly lower energy barriers, thus suggesting the use of this alternative pathway to predict whether a PKR on SWCNTs is favored or hampered. Accessible energy barriers of up to 16 kcal mol-1 are estimated and our results suggest that semiconducting SWCNTs react faster than metallic ones, although both types can be functionalized. Guided by our theoretical predictions, cyclopentenones are successfully attached to SWCNTs by heating and are, subsequently, characterized in the laboratory.

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Section: Introductionmentioning

confidence: 99%

Regioselectivity of the Pauson–Khand reaction in single-walled carbon nanotubes

et al. 2018

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“…Notably, this synthetic method also works for cyclic 1,6-allenynes to afford the diastereoselective construction of tricyclic products, which are challenging for classical synthetic methods and will be important for applications in drug and natural products synthesis. Although both 5- exo-dig and 6- endo-dig pathways are not surprising in metal-catalyzed alkyne closure 51–53 and it is quite common for those with gold catalysts to provide 5- exo-dig products 51,54–58 , it is very unusual for rhodium catalysts to favor a 5- exo-dig pathway 58 , thereby preferentially forming the proximal product (via 5/5 rhodacyclic intermediate) rather than the distal product (via 6/5 rhodacyclic intermediate) 59 . Our systematic DFT study provides an insight over the classical mechanistic pathways (such as initial 6- endo - dig cyclization, initial oxidative coupling between the alkyne and allene parts and C sp3 –H activation).…”

Section: Discussionmentioning

confidence: 99%

Enantioselective Rhodium-Catalyzed Cycloisomerization of 1,6-Allenynes to access 5/6-Fused Bicycle[4.3.0]nonadienes

et al. 2019

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Transition-metal-catalyzed cycloisomerization of 1,n-allenynes represents a powerful synthetic tool to rapidly assemble complex polycyclic skeletons from simple linear substrates. Nevertheless, there are no reports of the asymmetric version of these reactions. Moreover, most of these reactions proceed through a 6-endo-dig cyclization pathway, which preferentially delivers the distal product (via 5/5 rhodacyclic intermediate) rather than the proximal one (via 6/5 rhodacyclic intermediate). Herein, we report an enantioselective rhodium(I)-catalyzed cycloisomerization of 1,6-allenynes to provide the proximal product 5/6-fused bicycle[4.3.0]nonadienes in good yields and with excellent enantioselectivities. Remarkably, this chemistry works perfectly for 1,6-allenynes having a cyclic substituent within the allene component, thereby affording synthetically formidable tricyclic products with excellent enantioselectivities. Moreover, extensive DFT calculations suggest an uncommon pathway involving 5- exo - dig cycloisomerization, ring-expansion, rate-determining alkene isomerization involving C sp3 -H activation, C-C activation of the cyclobutene moiety and finally reductive elimination. Deuterium labeling experiments support the rate-determining step involving the C–H bond activation in this transformation.

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“…Pauson-Khand reaction involving an allene moiety is an excellent strategy to give cyclopentenones. 73,74 Reaction of enantiopure allenyne 98 in the presence of a zirconium catalyst has afforded bicycle[3.3.0]octenone 99 in 39% yield and 85% ee (Scheme 41). 75 The authors have explained that the loss of enantiomeric purity might be due to an isomerisation of the diastereomeric (Z)-α-alkylidene cyclopentenone to the (E)-α-alkylidene cyclopentenone.…”

Section: Metal-catalyzed or Metal-promoted Cyclizationsmentioning

confidence: 99%