Iminopyridinium ylides

With Af-acyl or Af-sulfonyl hydrazines as nucleophiles, Zincke salts serve as sources of iminopyridinium ylides and ylide precursors.Reaction of the nicotinamide-derived Zincke salt 8 with ethyl hydrazino urethane 42 provided salt 43, while the tosyl hydrazine gave ylide 44 (Scheme 8.4.14). ° Benzoyl hydrazines have also been used in reactions with Zincke salts under similar conditions.Af-amino-1,2,3,6-tetrahydropyridine derivatives such as 47 (Scheme 8.4.15), which showed antiinflammatory activity, are also accessible via this route, with borohydride reduction of the initially formed ylide 46. ... 

Polymers in Schemes 12 and 13 were the first examples of the preparation of pyridinium and iminopyridinium ylide polymers. One of the more recent contributions of Kondo and his colleagues [16] deals with the sensitization effect of l-ethoxycarbonyliminopyridinium ylide (IPYY) (Scheme 14) on the photopolymerization of vinyl monomers. Only acrylic monomers such as MMA and methyl acrylate (MA) were photoinitiated by IPYY, while vinylacetate (VA), acrylonitrile (AN), and styrene were unaffected by the initiator used. A free radical mechanism was confirmed by a kinetic study. The complex of IPYY and MMA was defined as an exciplex that served as a precursor of the initiating radical. This ylide is unique in being stabilized by the participation of a... 

A single paper from Charette and coworkers details the catalytic asymmetric hydrogenation of W-iminopyridinium ylides to substituted piperdines using PHOX ligand 82 in combination with iodine (Table 17) [81]. 

The process shown in the right half of Scheme 13 represents the selective ortho arylation of an iminopyridinium ylide, directed by the CO group, which affords adequate precursors of natural products [113, 114]. 

Krueger CA, Kuntz KW, Dzierba CD, Wirschun WG, Gleason JD, Snapper ML, Hoveyda AH (1999) J Am Chem Soc 121 4284 Legault CY, Charette AB (2005) Catalytic asymmetric hydrogenation of N-iminopyridinium ylides expedient approach to enantioenriched substituted... 

When a 1 2 mixture of triaminocyclopropenylium perchlorate and an iminopyridinium ylide in dimethylsulfoxide was heated at 80 C for 24 hours under nitrogen, cyclopropcniminc derivatives 5 were obtained in yields ranging from 10 to 35%. ... 

The triaminocyclopropenylium ions 1 were readily attacked by nitrogen nucleophiles, such as iminopyridinium ylides in dimethyl sulfoxide, to give the cyclopropeneimines 2 in moderate yields (see also Section 5.A.4.1.2.). 

Similarly, the trisulfanylcyclopropenylium ions 3 reacted with iminopyridinium ylides in dimethyl sulfoxide or with sulfonium ylides in tetrahydrofuran. In these reactions, double addition of the cyclopropenylium ion occurred to give the A,A -bis(cyclopropenylidene)urea derivatives 4. ... 

A mixture of l,2,3-tris(ethylsulfanyl)cyclopropenylium perchlorate (2.23 g, 7.0 mmol) and /V-benzoyl-iminopyridinium ylide (l.OOg, 5.1 mmol) in DMSO (30 mL) was stirred with heating at 80 C for 8 h under N2. After standing overnight, the solvent was removed under reduced pressure. The residue was chromatographed (silica gel) to afford a dark brown oil yield 0.78 g (60%). 

Table 10.17 Charette s enantioselective hydrogenation of N iminopyridinium ylides 6...

Larivee A, Mousseau JJ, Charette AB (2008) Palladium-catalyzed direct C-H arylation of iV-iminopyridinium ylides application to the synthesis of ( )-anabasine. 1 Am Chem Soc 130 52-54... 

Pyridinium and quinolinium ylides undergo many of the reactions associated with N-oxides. N-Iminopyridinium ylides, for example, are readily converted into IH-l, 2-diazepines, whereas until recently AMminoquinolinium ylides and analogous isoquinolinium ylides had given only 2-aminoquinolines and 1-amino-isoquinolines, respectively. Irradiation of the iV-iminoquinolinium ylide dimers... 

Another important example of a resist based on radiation-induced polarity change employs the photochemical transformation of N-iminopyridinium ylides (XXII) to 1,2-diazepines (XXIII) as the basis of a negative non-chemically amplified resist (Scheme 6.14). ... 

Scheme 6.14 Photochemical transformation of N-iminopyridinium ylides. 6.3.4.S Diazo resists...

Mesitylenesulphonylhydroxylamine (MSH) reacts with IcP 478 to give iV-amino-IcP 479 that converts into 7V-iminopyridinium ylide 480 when treated with ethyl chloroformate and potassium carbonate. Ultraviolet irradiation of this ylide gives a mixture of acylated amines 481 and 482 (86T1511). 

The photochemical reaction of Y-iminopyridinium ylide (147) has given isomeric 1,2-diazepines (86) and (148) (Equation (23)) the ratio of which was solvent-dependent. The success of this reaction contrasts with the photoinduced rearrangement of similar A -iminopyridinium ylides from bicycles. 

Reactions with A/-acyl or AAsulfonyl hydrazines gave rise to iminopyridinium ylides and ylide precursors such as 43 and 44. " Benzwl hydrazines are also used in the Zincke reaction under simitar conditions. ... 

Direct Arylation, The direct functionalization of electron-deficient heteroarenes, such as pyridines, is a challenging process. Instead, methodologies have been developed that employ pyridine (V-oxides or IV-iminopyridinium ylides, in the presence of Pd(OAc)2 and a bulky phosphine ligand (eqs 138 and 139). The coupling partners involve a variety of aryl halides and triflates, and the reaction conditions can be extended to other azine-derivatives. Both the JV-oxide and pyridinium ylide moieties can be deprotected under reductive conditionsAryl tosylates have also been reported as good coupling partners for pyridine JV-oxides. ... 

V-Iminopyridinium ylides react with alkenyl iodides, alkenyl bromides, or alkynes to form 2- and 2,3-substituted pyrazolo[ 1,5-alpyridines through a direct alk)mylation followed by cyclization under PdBr2-P(4-MeOPh)3-AgOBz conditions. Mechanistic studies revealed that alkenyl halides are converted to alkynes under the reaction conditions. The reaction scope works well over a range of alkyl and aryl alkynes as well as p3nidiniutns (eq39). 

Arylation with bromobenzene of the activated pyridine is then carried out in the presence of palladium acetate (5 mol %), tri-r-butylphosphine (15 mol%), and potassium carbonate under anhydrous conditions. The arylated. V-iminopyridinium ylide is afforded in 80% yield as a sole isomer and it can be reduced efficiently to the corresponding pyridine under known conditions. Interestingly, the competition experiment to compare the difference of reactivity between pyridine iV-oxide and the V-iminopyridinium ylide shows that pyridine iV-oxide is not arylated, while 56% of arylated V-iminopyridinium ylide is obtained. In addition, bis-arylation is observed in less than 10% yield. These... 

The synthesis of 2- and 2,3-substituted pyrazolo[l,5-a]pyridines proceed via a two-step procedure. For instance, to form 2-[4-(benzyloxy)phenyl]pyrazolo[l,5-a]pyridine, the stepwise method involves (i) the activation of pyridine to generate iV-benzoylitninopyridinium ylide as already described and (ii) a palladium-mediated C2 alkenylation of the iminopyridinium ylide in the presence of (. -(2-iodovinyl)(4-benzyloxy)benzene, silver benzoate (3 equiv), and palladium dibromide (5 mol %)/tris(4-methoxyphenyl)phosphine (10 mol%) as a catalytic system (eq 38). The second step (i.e., the C-H alkenylation step) delivers the desired product in 87% step after 16 h at 125 °C in 1,4-dioxane. 

Palladium-catalyzed Arylation of Pyridine N-Oxides and N-Iminopyridinium Ylides. Tri-tert-butylphosphine has been used in the palladium-catalyzed C-arylation of pyridine 7/-oxides and derivatives. Using palladium acetate as the catalyst, tri-tert-butylphosphine as the ligand, and 3-bromopyridine as the electrophile, the C-H arylation of pyridine tV-oxide was accomplished, yielding the 2-arylated compound as the major product and the 2,6-diarylated pyridine as a minor product (eq 24). ... 

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