Asymmetric 13-dipolar cycloaddition of nitrones with ketene acetals catalyzed by chiral oxazaborolidines

Naked d-orbital in a centrochiral Ni(II) complex as a catalyst for asymmetric [3+2] cycloaddition

“…When the reaction was performed using 2a with vinyl ether 5 instead of 1a , no reaction took place (Fig. 7a); this is complementary to the reported IED [3+2] cycloadditions25262728293031323334, and supports the validity of our working model, which involves a Ni(II)–enolate as the active dipolarophile. The observation that no reaction occurred when we applied the catalytic system to the reaction of ( Z )- 6 and 1a (Fig.…”

“…(ii) Catalytic asymmetric [3+2] cycloaddition using transient enolate has yet to be developed, despite the long history of enolate studies253839. Only a few IED cycloadditions with electron-rich alkenes (such as enol ethers and silyl ethers), not enolate, have been reported with asymmetric catalysts25262728293031323334. The [3+2] cycloaddition, which is controlled by the lowest unoccupied molecular orbital of the dipole and the highest occupied molecular orbital of the 1,3-dipolarophile, can be also categorized as ‘type III' according to Sustmann's classification40.…”

“…1c). This report provides insights into the elusive mechanistic basis for inverse-electron-demand (IED) [3+2] cycloaddition25262728293031323334 of α-ketoesters with ( E )-nitrones (Fig. 1d).…”

Asymmetric Metal‐Catalyzed 1,3‐Dipolar Cycloaddition Reactions

“…Scheeren et al reported the first enantioselective metal-catalyzed 1,3-dipolar cycloaddition reaction of nitrones with alkenes in 1994 [26]. Their approach involved C,N-diphenylnitrone 1a and ketene acetals 2, in the presence of the amino acidderived oxazaborolidinones 3 as the catalyst (Scheme 6.8).…”

Catalytic Asymmetric 1,3‐Dipolar Cycloaddition of Nitrones to Alkylidene Malonates: Highly Enantioselective Synthesis of Multisubstituted Isoxazolidines

“…Furthermore, the corresponding isoxazolidines are particularly useful synthetic intermediates for various natural products, [2] in which they are the framework of many biologically active compounds, such as antifungal, [3] anti-tuberculosis, [4] and antiviral agents . [5] Since the pioneering works of Scheeren [6] and Jørgensen in 1994, [7] chiral metal complexes [8][9][10][11][12] as well as organic catalysts [13] have been successfully developed for the catalytic asymmetric 1,3-dipolar cylcloaddition of nitrones to alkenes. Nevertheless, the alkene part was always limited to N-alkenoyl amides and generally a high catalyst loading was necessary.…”