Ylides, pyridazinium

Besides removal of alkyl-based groups located at the N-2 of a pyridazin-3(27/)-one also real reactions in the side chain appeared. Pyridazinium ylides, obtained via deprotonation of iV-alkylpyridazinium salts, have been reacted with phenyl isocyanates and benzenediazonium salts <2002MI287, 1997T4411>. As discussed in Section 8.01.5.7.2 1,3-dipolar cycloaddition with ethyl acrylate and ethyl propiolate were also studied. 

Halophenyl)pyridazinium ylides have been found to act as strong carbon nucleophiles towards diazoaromatic compounds to yield stable carbanion disubstituted ylides for which the intense colour has been attributed to intramolecular charge transfers.88... 

Resonance-stabilized anions are also obtained if methyl groups at positions I or 4 in the pyridazine part of 2//-cyclopenta[d]pyridazine are deprotonated [78H(11)387]. Pyridazinium ylides readily undergo 1,3-dipolar cycloaddition reactions [77CPB192 79H(I2)661 81JCS(P1)73 87BCJ3645]. 

Ionization constants of hydroxy- and mercaptopyridazines, ° of amino- and diaminopyridazines and their quaternization products,of methylsulfinylpyridazines," and of pyridazinium ylides have been recorded. The basicities of a series of pyridazines have been determined and correlated with substituent constants using the Hammett free-energy relationship. The magnetic susceptibility of pyridazine was measured, and the rate constant for the reaction of hydrogen atoms with pyridazine was determined. The experimental dipole moment, Kerr constant, and molar Cotton-Mouton constant, obtained at 298 K and 633 nm, are reported. The magnetic circular dichroism spectrum of pyridazine has been measured. ... 

Pyridazinium and phthalazinium dicyanomethylides give indolizines as primary adducts with 1,2,3-triphenylcyclopropene, either by [4 + 2] cycloaddition or by 1,3-dipolar addition of the ylide to triphenylcyclopropene (81JCS(P1)73). 

Mangalagiu studied the regioselectivity of the 1,3-dipolar cycloaddition of several pyridazinium methylides 105 to ethyl acrylate, ethyl propiolate, and acrylonitrile. The reaction is HOMO controlled from ylides and only one regioisomer 106 (major isomer as and minor isomer trans) or 107 is formed, namely the one in which the ylide carbanion makes a new bond with the most electrophilic carbon of the 1,3-dipolarophile. In some cases oxidation of 106 to 107 is observed in the reaction mixture in contact with the air (Scheme 23), which can be avoided by working in N2 atmosphere <1996T8853, 1997ACS927, 1999EJO3501>. 

The thiazolo[3,2-h]pyridazinium salts 192 react with active methylene compounds to give ylides 1%. This reaction is initiated by nucleophilic attack at C-8 and subsequent deprotonation to 194, which is oxidized by atmospheric oxygen via radical intermediates 195 (82CPB35) (Scheme 34). 

Although some pyridinium ylides and pyridazinium N-oxide do not form adducts with tetrachlorocyclopropene, compounds (321, Z = NCOR, NC02R or C(CN2)) do form moderate to low yields of adducts, eg. (322). This compound undergoes an interesting elimination of AcCl on heating, the a-b bond being cleaved to lead, after proton transfer, to (323) 253>. 

In a related reaction, pyridazinium C-ylides underwent addition to tetrachlorocyclopropene to give an exo-product 13, the stereochemistry of which was established by X-ray crystallography similarly, addition to 1,2,3-triphenylcyclopropene gave 14, 15a, and 15b. " ... 

Perhalocyclopropenes underwent dipolar cycioaddition to pyridazinium A-ylides to give isol-able diazabicyclo[3.1.0]hexanes 19.286,287... 

Pyridazinium A-ylide (213) underwent 1,3-dipolar cycloaddition with the perhalocyclopropene (214) to give the cycloadduct (215) which was thermolysed in refluxing xylene to give (128) <86CPB1023>. Flash vacuum pyrolysis, at temperatures between 450°C and 700°C, of the A-pyrazolyl derivative (216) gave a mixture of two products (217) and (218). The relative proportions of these two products were shown to be temperature dependent. The major product at higher temperature was shown to be (217), whereas at lower temperatures (218) predominated <93CC840>. 

In the reaction of 2-bromo-3,3,3-trifluoropropene with pyridinium ylides cycloaddition occurred readily leading to I-CF3 derivatives of indolizines [21]. Similar reaction took place in the cases of pyridazinium and isoquinolinium ylides. 

---