N ylide

Azolinones, azolinethiones, azolinimines N-Oxides, N-imides, N-ylides of azoles Thermal and Photochemical Reactions Formally Involving No Other Species 2.1 Thermal fragmentation... 

MI1 I. Zugravesku and M. Petrovanu, in N-Ylide Chemistry", McGraw... 

Contrary to the allyldimethylamines, the less nucleophilic l-morpholino-2-butene 117 and 3-morpholino-l-butene 118 do not yield products derived from an intermediary N-ylide rather, allylic C/H insertion products were isolated (see Sect. 2.3.3)151). 

Reaction of the imine moiety of 278 with excess ethyl diazoacetate in the presence of Cu(acac)2 led to the cyclopentane-annulated product 279 the structure of which was confirmed by an X-ray analysis 262. It is assumed that 279 results from reaction between a carbene dimer (diethyl fumarate) and an intermediate N-ylide or the... 

Thermolysis of 1-imidoyliminopyridinium N-ylides 109 gave the pyrido-triazines 110 in addition to 111 and 112 (76CL413 77JOC443). Compounds 109 were obtained by the reaction of pyridinium salts 107 with 108. 

Hu and co-workers reported a facile synthesis of pyrrolo[2,l-n]phthalazine 205 by a 13-dipolar cycloaddition of phthalazium N-ylides generated from 203 with electron deficient alkenes to give 204, followed by treating 204 with tetrakispyridine cobalt(II) dichromate [Py4Co(HCr04)2, TPCD] to complete the aromatization <00JHC1165>. 

Whereas in Wmethyl-4,6-dimethylpyrimidinium ion the covalent addition takes place at C-6, it is assumed that 30 also undergoes covalent hydrazina-tion at C-6. However, the formation of dimer 32 shows the high sensitivity of C-2 in 30 for addition of nucleophiles, and it leads to the daring suggestion that it is the resonance-stabilized ylide 31 that probably is the active species undergoing addition at C-2 (Scheme III. 19). It was calculated (80UP1) that the reactivity at C-2 in the N-ylide 31 is greater than that at C-2 in the Waminopyrimidinium salt 30. 

N-Nukleophile, speziell N-haltige Heterocyclen, addieren sich an Tetracyan-oxiran. Unter Eli-minierung von 2-Oxo-malonsaure-dinitril entstehen die entsprechenden N-Ylide z.B.507 ... 

It was formerly considered that nitrenes attack only the carbons atom of thiophene (84CHEC-(4)74i). Since 1984, several S,N-ylides formed by the attack of a nitrene on the ring sulfur atom of thiophene have been prepared (89AHC(45)l5l). Thus, ethoxycarbonyl nitrene with polyhalogenothiophenes forms the S,N-ylide (46) in 44% yield (84CC190). The X-ray crystal structure reveals that the sulfur in such ylides is pyramidal. 

Thiophene S,N-ylides are comparable with the 1-mono- and 1,1-dioxides in that they exhibit diene rather than aromatic properties (86JCS(P 1)233). The S,C-ylides appear to be more sluggish in cycloaddition reactions and are therefore considered more aromatic . 

Photochemistry as a Tool in Heterocyclic Synthesis From Pyridinium N-Ylides to Diazepins and Beyond J. Streith, Heterocycles, 1977, 6, 2021-2043. 

Scheme 10.25 Cyclopropanation of an a,/ -unsaturated ester using a N-ylide.

Scheme 10.26 N-ylide-catalyzed asymmetric intramolecular cyclopropanation.

Fig. 10.5 Catalytic asymmetric cyclopropanation using N-ylides derived from 53a-d. Catalyst, yield (% ee) are shown for each product. 53a,c favored the (+)-enantiomer, while 53b,d favored the (—)-enantiomer in all cases.

Scheme 10.27 Proposed mechanism for N-ylide-mediated catalytic cyclopropanation.

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