Hexafluoroacetone azine

Hexafluoroacetone azine accepts nucleophiles (ROH, RSH, R NH) in positions 1 and 2 to yield hydrazones [27] Phosphites give open-chain products via a skeletal rearrangement [22] Radical addition reactions are also reported [22] Treatment of tnfluoropyruvates with tosylhydrazine and phosphorus oxychlo-ride-pyndme yields tnfluoromethyl-substituted diazo compounds [24] (equation 3)... 

The first example of a cycloaddition reaction of a multiple bond to a diene was reported in 1917 Surprisingly, it was found that benzal azine adds to 2 equivalents of several unsaturated systems, when offered in excess, to yield bicyclie compounds. This reaction was named criss-cross" cycloaddition [190], Exploitation of the preparative potential of criss-cross cycloaddition began only in the early 1970s, when hexafluoroacetone azine became available on a larger scale [191,192] The study of this reaction proved to be an impetus tor the development of azine chemistry [183, 193]... 

Hexafluoroacetone azine reacts with 2 equivalents of terminal olefins [194] and acetylenes [182] to give 1,5-diazabicyclo[3.3.0]octanes and 1,5-diazahicy-clo[3 3 0]octa-2,6-dienes, respectively (equation 44). 

An unusual 1,4-migration of a trifluoromethyl group was observed when azomethine imines were synthesized from hexafluoroacetone azine and alkoxy-acetylenes The rearrangement, which occurs at temperatures as low as 0 "C, results in the formation of A-(perfluoro-ferf-butyl)pyrazoles [207] (equation 46)... 

Simple criss-cross cycloadditions described so far are in fact limited to aromatic aldazines and cyclic or fluorinated ketazines. Other examples are rather rare, including the products of intramolecular criss-cross cycloaddition. The criss-cross cycloadditions of hexafluoroacetone azine are probably the best studied reaction of this type. It has been observed that with azomethine imides 291 derived from hexafluoroacetone azine 290 and C(5)-C(7) cycloalkenes < 1975J(P 1)1902, 1979T389>, a rearrangement to 177-3-pyrazolines 292 competes with the criss-cross adduct 293 formation (Scheme 39). 

The reaction of hexafluoroacetone azine with cycloheptatriene at 70 °C provides after 8 days a mixture containing 28% of unchanged azine 290 and products formed by three distinct mechanistic pathways, that is, criss-cross cycloaddition product 294, a bis-ene adduct 295 and its oxidation product 296, and [3+6] cycloaddition leading to diaziridine 297, in the ratio 15 38 7 (Scheme 40) <1995JFC(73)203>. 

The reaction of quadricyclane with hexafluoroacetone azine 290 under similar conditions affords a mixture of a 1 1 adduct 298, the o , -bis-cycloadduct 299 formed by reaction of the C=N bond in 298 with quadricyclane, and the criss-cross addition product 300 (Scheme 41) <1995JFC(72)147>. 

A simple preparative route to the previously unknown lff-3-pyrazolines via azomethine lmines was developed. Olefins of the type r cH=CHR2 react with hexafluoroacetone azine to give azomethine imines, which undergo a sequence of prototropic shifts to form l//-3-pyrazolines [196, 202]. On heating, the latter are transformed into 3-trifluoromethylpyrazoles [196, 206] and, on treatment with bases, into 1,2,5,6-tetrahydropynmidines [206] (equation 45)... 

The azomethine imine 145 from isobutylene and hexafluoroacetone azine, with DMAD, leads to a stable 1 1 adduct (146) in 90% yield.132,133... 

The so-called criss-cross additions of azines involve a sequence of two 1,3-dipolar cycloaddition reactions, as exemplified by the reactions of hexafluoroacetone azine and benzaldazine with DMAD and phenyl isocyanate (Scheme 9) (76S349). 

What is the product C10H4FI2N2 of the reaction of hexafluoroacetone azine with two molecules of acetylene ... 

The reaction shown above is a bizarre example of a crisscross cycloaddition. It starts as a (2 + 3) cycloaddition of one molecule of acetylene to positions 1 and 3 of the hexafluoroacetone azine to form an intermediate that by another (2 + 3) addition of another molecule of acetylene across the remaining nitrogen-carbon double bond forms another five-membered ring. In this way, a bicyclic system of two five-membered rings is formed to yield the final product [124, 125]. 

Enamines possessing /7-hydrogen atoms add hexafluoroacetone azine to form transient dipolar azomethine imines 9, as evidenced by low-temperature 19F NMR spectroscopy, which rearrange to hydrazones. If there is no hydrogen atom in the /7-position the betaines cyclize to unstable derivatives 10 of azetidine (equation 7)24. 

Based on this concept, a preparatively simple route to the previously unknown l//-3-pyrazolines was developed. Olefins of type RCH=CHR and hexafluoroacetone azine react to give azomethine imines, which subsequently are transformed in a series of prototropic shifts to give 1//-3-pyrazolines [75JCS(P1)538 79T389]. The latter on heating with AIBN undergo fluoroform elimination with heteroaromatization to yield trifluor-omethyl-substituted pyrazoles [82JFC(I9)437] (Scheme 63). 

Since the criss-cross cycloaddition reaction is a sequence of two [3 + 2] cycloaddition steps, the reaction of hexafluoroacetone azine with a,a>-diolefins offers access to a new class of trifluoromethyl-substituted heterocyclic macromolecules. Polymers with interesting structures and properties become available by criss-cross polymerization (88MI3 89MI2 90MI2). 

Alkenes, perfluoro-cycloadditions to benzyl azide, 60, 35 pyridine imines and ylids, 60, 36 Alkenes, perfluoro-, as heterocyclic precursors, 59, 10 Alkylation, free-radical, of 1,3-dimethyluracil, 55, 227 A-Alkylation, [ 1,2,4]triazolo[ 1,5-u)-pyrimidines, 57, 110 Alkynes, photocycloaddition to uracils, rearrangement with HCNO elimination, 55, 149 Alkynes, ethoxy-, cyclaoddition to hexafluoroacetone azine, 60, 32 Alkynes, perfluoro-, as heterocyclic precursors, 59, 10 Allenes... 

A specific type of [3 -I- 2] cycloaddition reaction is the crisscross cycloadditioii between the electron-deficient hexafluoroacetone azine (6) and an electron-rich, terminal alkene or al-kyne. - Reactions can be performed under thermal or photochemical conditions and 2 1 adducts are obtained in good yields. 

Hexafluoroacetone azine underwent thermally induced reaction with alkenes to give nonstereo-specifically l,l-bis(trifluoromethyl)cyc)opropanes 1 and 2 in low yield and presumably by a radical pathway. -... 

The 1 1 adducts formed from phosphites and hexafluoroacetone azine, originally considered to be quinquecovalent phosphoranes containing phosphorus as part of a three-membered ring, have now been shown by X-t y analysis to be iminophosphoranes (13). ... 

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