Recent Advances of Catalytic Asymmetric 1,3-Dipolar Cycloadditions

Abstract

Scheme 7. Chiral Ni-Catalyzed 1,3-DC of Nitrones Scheme 8. Use of α′-Hydroxy Enones as Dipolarophile Scheme 9. Use of 2-Alkenoyl Imidazoles Scheme 10. Use of α′-Phosphoric Enones Scheme 11. Use of Alkenoyl Pyridine N-Oxides

1,3-Dipolar Cycloaddition Reactions of Azomethine Ylides with Carbonyl Dipolarophiles Yielding Oxazolidine Derivatives

“…The reaction of imine 217 with ethyl diazoacetate (218) catalyzed by 10 mol % of Cu(tfacac) 2 , in refluxing benzene, led to formation of azomethine ylide intermediate 5c which underwent intramolecular cycloaddition onto the ester carbonyl to produce both endo and exo isomers of 219, isolated in 13% and 14% yield, respectively. In refluxing CH 2 Cl 2 , endo-219 was obtained in 36% yield, whereas with the use of a stoichiometric amount of Cu(tfacac) 2 , a 41% yield of endo-219 resulted. The latter conditions were applied to a wide range of imines (Table 29).…”

“…The versatile and convergent nature of the 1,3-dipolar cycloaddition reaction has led to its development as a powerful method for the synthesis of five-membered heterocycles [1][2][3][4][5][6][7]. The reaction involves the addition of 1,3-dipoles, such as azides, nitrones, carbonyl ylides, nitrile oxides, nitrile imines and azomethine ylides to unsaturated double or triple bonds (1,2-dipolarophiles) [8][9][10][11][12][13][14][15].…”

Oxidative cyclizations of oximes using hypervalent iodine reagents

“…[17][18][19] In particular, the reaction of various aldoximes with alkynes in the presence of organohypervalent iodine(III) reagents such as DIB, 48,51,[54][55][56][57] BTI, 46,58,59 Koser's reagent, 49,60 or PhIO, 27,61 leads to oxidative heterocyclization yielding the corresponding isoxazoles. This procedure is applicable to various internal or terminal alkynes under mild condition.…”

“…[12][13][14][15][16] Aldoximes and ketoximes are convenient and readily available starting materials for construction of various heterocyclic compounds with nitrogen and oxygen in the ring, which are commonly found in medicinal drugs, bioactive compounds, and natural products. [17][18][19][20][21][22][23][24][25][26] The oxidation of aldoximes 1 using hypervalent iodine(III) reagents 2 produces nitrile oxides 3, which can react in situ with appropriate dipolarophiles such as alkenes 4, alkynes 5, nitriles 6, or aldehydes 7 via the intermolecular 1,3-dipolar cycloaddition to give the corresponding heterocyclic products such as isoxazolines 8, isoxazoles 9, oxadiazoles 10, or dioxazoles 11 (Scheme 1). 13,27 Scheme 1.…”

First example of an organocatalytic asymmetric Mannich reaction between aldimines of glycinates and sulphonyl imines

“…In fact, aldimines of glycinates were precursors of azomethine ylide, widely used in the asymmetric 1,3-dipolar cycloaddition with various dipoalrophiles. [21][22][23][24][25] More recently, Carretero and co-workers have described the Fesulphos-Cu I catalyzed asymmetric direct Mannich reaction with aldimines of glycinates. 26 The obtained unstable Mannich products need in situ selective reduction of imines to the amino group.…”