Hexafluoroacetone azine, cycloadditions

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]... 

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 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). 

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]. 

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 undergoes cycloaddition reactions with various electron-rich olefins or 1,3-dienes at moderate temperature to givepyridazines [Eq. (6)]. Depending on the structure and the quantity of the olefin employed and the temperature, other mono or bicyclic heterocycles can be formed. 

Fluoroalkylketenimines may be obtained from fluorinated alkenes and 60 undergoes a series of cycloaddition reactions, including formation of the quinoline derivative 61.149 Hexafluoroacetone azine (62) also reacts with acetylenes150 and the formation of pyrazoles (63) has been formulated as involving the quite novel migration of a trifluoromethyl group. 

Hexafluoroacetone azine reacts with two equivalents of terminal olefins (71JCS(C)2404) and with acetylene derivatives (75TL1125), forming 1,5-diazabicy-clo[3.3.0]octenes and l,5-diazabicyclo[3.3.0]octa-2,6-dienes 27, respectively (Scheme 27). The cycloaddition involves two [3 + 2] processes. The structure of azamethineimine is confirmed by X-ray analysis data (74AGE475). 

Plaza-Compounds. The criss-cross cycloaddition of JN-phenylmaleimide to benzal-dehyde azine, PhCH=NN CHPh, results in the pyrazolopyrazole-derivative (485) 432 hexafluoroacetone azine and ethyl acrylate or ethyl vinyl ether similarly yield the [l + 2] adducts (486 R = COOEt or OEt, respectively).433 — Compound (487) opens to the ylide (488) on heating in the presence of tetracyanoethylene the 4 + 2 ] cycloadduct (489) is formed, which fragments spontaneously to the beta-ine (490) and the diene (F,C),OCHCH-C(CN),. Thermolysis of the diazabicyclo-... 

Criss-cross cycloaddition reactions with hexafluoroacetone azine to give partially fluorinated heterocycles and polymers 06H(67)443. gem-Disubstituent effect in formation of heterocycles 05CRV1735. 

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