Imine ylide

The reaction of 410 with dimethyl acetylenedicarboxylate yields 411 (78TL1291). Since 410 can be represented as the azomethine ylide 412 or the azomethine-imine ylide 413, this result may indicate that the azomethine ylide is more reactive in cycloadditions with acetylenes than azomethine-imine ylide s. 

Triphenylthieno[3,4-c]pyrazole (414) can be presented as a hybrid of dipolar-contributing azomethine imine ylide (415) or thiocarbonyl ylide canonical forms 416. Upon reacting this ylide with electron-poor olefins, it behaved like a thiocarbonyl ylide. Thus, with maleimide, a mixture of endo (419) and exo adducts (420) were obtained (74JA4276), which resulted from addition at the thiocarbonyl moiety. The reaction of 414 with dimethyl acetylenedicarboxylate gives the desulfurized indazole 418 in addition to the adduct 417 (Scheme 41). 

Imine ylides 7 and carbonyl ylides 8 are not stable but may be generated in situ by pyrolysis of suitably substituted aziridines and oxiranes. The energy of the HOMO, and therefore the nucleophilicity of the parent 18-electron dipoles, decreases from very high to very low across the series 7-18. In the same series, the electrophilicity increases from moderate to high, being consistently higher when the central atom is oxygen. 

Furans (133) are obtained from acyltriafulvenes [(acylmethylene)cyclopropenes] (131) and azomethine-imines, -ylides or oxides (132) (75TL3919). The reaction involves the transfer of the group X from the azomethine dipole to the triafulvene and may proceed as shown in Scheme 28. I... 

Rs Imine ylide 0 R4 8 Carbonyl ylide 9 R4 Rj O R3 10 Carbonyl inline... 

The non-classical system (182) has been synthesized, starting from 4,5-bis(chloromethyl)-l,2,5-thiadiazole, and characterized by the isolation of its dimer and adducts. The more complex but stable non-classical thiophens (183)—(185) have been prepared, starting from azomethine imine ylides, generated in situ from 1-aminopyridinium, 1-aminoquinolinium, or... 

Table 2.14 Theoretical basicity values for phosphorus imines, ylides and phosphines ...

Phenylperhydro-l,3,4-oxadiazin-2-ones 151 react with aliphatic or aromatic aldehydes or ethyl 2-oxoacetate to give the intermediates 152. The azomethine imine ylides 152 yield primary oxazolidines 153 <200081170, 2002S1885, 2004TL3127>. These compounds can be synthesized also by treatment of 151 with ethyl oxoacetate or aldehydes in the presence of magnesium bromide etherate. The tandem cycloreversion-cycloaddition of 153 with various electron-poor dipolarophiles then leads to pyrazolidines 154-156 (Scheme 22). 

Intramolecular cyclisation of nitrile imine ylides occurs when 2-pyridyl- (22 X= CH) or 3-pyridazinylhydrazones (22 X= N) are treated with chloramine-T to yield 1,2,4-triazolo[4,3-a] pyridines (23 X= CH) and l,2,4-triazolo[4,3-l>]pyridazines (23 X= N) in a simple one-pot synthesis [93SC319S]. 

Lately, Soliman et al. [67] replaced isocyanates in the above reactions by the monoanils of benzil (90), o-naphthoquinone or triketones (such as 91) only to obtain the corresponding azetidinones (92, 93) with each of ylides 2, 82 or 88 (Scheme 19). However, reactions were not run at 2 1 (imine ylide) stoichiometry. 

Highly functionalized, biologically important 1,2,4,5-tetrazepine derivatives 256 have been prepared in the first example of a catalyst-free [4 + 3] cycloaddition reaction between in situ formed 1,2-diaza-l, 3-dienes and C,N-cyclic azomethine imine ylides 255 (13CC7905). After reaction optimization and substrate scope studies, this catalyst-free [4 + 3] cycloaddition was extended to the use of cychc hydrazones as substrates, such as 254a and 254b, which form the in situ generated azoalkenes, to yield the respective polycyclic products 256. 

For the reaction with a stabilized phosphoniutn ylide, the betaine intermediate undergoes proton transfer and even extrudes a sulfonamide group to give a vinyl phosphonium salt that can be trapped with water, a stabilized phosphonium yUde [223], or nitromethane (solvent) [225]. These findings suggest that the conversion of the betaine to the azaphosphetane is much slower than the interconversion between the two betaine diastereomers (Scheme 49). Thus, the Z/E ratio for the alkene product does not correspond to the diastereoselectivity for the initial imine/ ylide addition. Instead, the Z/E selectivity is decided by the different rates for the transformation of the two betaine diastereomers into their corresponding azaphosphetanes. 

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