Azomethine imines, cycloaddition with

Chen extended the scope of his iminium ion catalysed [3+2] cycloaddition with azomethine imines (see Sect. 2.1.2) to encompass cyclic a,P-unsaturated ketone substrates using primary amine 147 as the catalyst [194]. Interestingly, the presence... 

Pyrrolo annulated triazine 77 was prepared (88TL4415) by the [6 + 4]-cycloaddition of azoniafulvene ion 76 with azomethine imines generated from benzylidene phenylhydrazone (Scheme 19). 

Scheme 11 [3+2] Cycloaddition of azomethine imines with a,P-unsaturated aldehydes...

Copper-catalyzed 1,3-dipolar cycloaddition of azomethine imine 264 with ethyl propiolate 265 with a chiral ferrocenyl bidentate ligand efficiently generated dihydropyrazol[l,2- 7]pyrazolones 266 in very good yields and ee... 

Shintani and Fu repored enantioselective coupling of terminal alkynes 420 with azomethine imines 419 by copper-catalyzed [3 + 2]-cycloaddition (Scheme 133).195 In the presence of Cul and phosphafer-... 

Asymmetric [3 + 2] cycloaddition of azomethine imines with aliphatic traws-enals catalysed by prolinols. 

The Chi group recently achieved the first NHC-eatalyzed diastereo- and enantioselective [3 + 4] cycloaddition of azomethine imines and enals via 1,4-dipolarophile intermediates generated by oxidative catalytic remote y-car-bon aetivation of enals. Dinitrogen fused seven-membered heterocyclic products were produced with high enantiomerie purity (up to 81% yield and 99% ee). Racemic azomethine imines ean be used as 1,3-dipolar substrates to afford dinitrogen-fused seven-membered heterocyclic compounds with high enantiomeric purity (s-factor up to 339). The key vinyl enolate intermediate is generated by oxidative y-carbon activation of enal via NHC catalysis as the reactive 1,4-dipolarophile (Scheme 7.116). 

SCHEME 11.47. Organocatalytic [3-1-2] cycloadditions of azomethine imines with... 

In 2006 Chen et al. [128] reported the first organocatalyzed stereoselective [3 + 2] dipolar cycloaddition of azomethine imines with aliphatic a,p-unsaturated aldehydes using chiral secondary amine catalyst 59. The desired cycloaddition products were obtained with good yields, good diastereoselectivities and good enantioselectivities for both electron-rich and electron-poor aromatic azomethine imines. In contrast, aliphatic azomethine imines (R = -Pr) led to poorer results (40% yield and 77% ee). Investigation of a variety of solvents and additives revealed that tetrahydrofurane/HaO mixture and 10 mol% of trifluoroacetic acid were preferred. No reaction was observed when aromatic a,p-unsaturated aldehydes were used. The authors proposed an iminium ion mechanism that could proceed via the transition states shown in Scheme 11.47. 

Sommer et al. found that Cu(I)-exchanged zeolites (Cu(l)-USY) could be utilized as heterogeneous catalysts for [3 + 2] cycloaddition of azomethine imines with terminal alkynes (Scheme 4.20). This method provides an efficient, versatile, and highly regi-oselective approach to Af,Af-bicyclic pyrazolidinone derivatives, which might exhibit useful bioactivities. The catalysts were readily available, convenient to remove, and reusable (Keller et al., 2009). 

The 1,3-dipolar cycloaddition of azomethine imines with alkynes could also be well facilitated by an Al203-supported copper hydroxide [Cu(0H) /Al203] (Scheme 4.21). Generally, the desired pyrazolidinones were obtained in good to excellent yields (Yoshimura et al., 2011). 

Scheme 1.12 Cycloaddition of azomethine imines with 3-acryloyloxazolidin-2-ones.

Dipolar cycloaddition of azomethine imine or nitrile imine-type dipoles with alkenes or alkynes yields nitrogen heterocycles containing two nitrogen atoms in the ring. MeOPEG resin was applied in the solid-phase synthesis of pyrazolines (Scheme 11.13). Resin-bound... 

Intramolecular cycloaddition of azomethine imines and olefins has been used to synthesize various diazabicyclic systems (Scheme 29). A double Diels-Alder addition of coumalic acid with butadienes has been used to prepare tricyclo[3,2,l,0 ]oct-3-enes (475). ... 

Kobayashi and co-workers successfully achieved the asymmetric 1,3-dipolar cycloaddition reaction of azomethine imines with terminal alkynes catalyzed by CuHMDS and DIP-BINAP ligand to provide N,N-bicyclic pyrazolidinone derivatives in high yields with exclusive regioselectivity and excellent enantioselectivity (Scheme 26) [46]. Mechanistic studies elucidated a stepwise reaction pathway and revealed that the steric character of the ligand determines the regioselectivity. Arai and co-workers applied chiral bis(imidazolidine)pyridine-CuOAc complex to the [3+2]cycloaddition of azomethine imines with propiolates for the construction of bicyclic pyrazolo[l,2-a]pyrazolone derivatives with up to 74% ee [47]. 

Scheme 28 Asymmetric [3-1-3] cycloaddition of azomethine ylides with azomethine imines...

In 2013, Wang and co-workers presented the first highly diastereo- and enantioselective [3-1-3] cycloaddition of azomethine ylides with azomethine imines employing Cu(l)/Bu-Phosferrox complex as the catalyst (Scheme 28) [49]. A wide range of azomethine ylides and azomethine imines, including those derived from aliphatic aldehydes, underwent this reaction to furnish the biologically active 1,2,4-... 

The 1,3-DC of azomethine imines and alkenes provides a straightforward access to dihydropyrazoles. In 2005, Sibi and coworkers developed the first catalytic enan-tioselective [3 -l- 2] cycloadditions of hydrazonyl bromide or chloride 31 to olefins 30 [19]. The corresponding dihydropyrazoles 32 were obtained in highly enantioen-riched form with 82-98% yields (Scheme 2.10). A concerted reaction mechanism was proposed considering the fact that only anti diastereomers of the cycloaddition products were observed by NMR analysis. Besides, other alkenes such as vinyl ether [20] and methallyl alcohol ether [21 ] were also good partners in the chiral Lewis acid-catalyzed cycloadditions of azomethine imines. 

F. Shi, R. Mancuso, R.C. Larock, 1,3-Dipolar cycloaddition of arynes with azomethine imines synthesis of l,2-dihydropyrazolo[l,2-a]inda-... 

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