Criss-cross cycloaddition

Reactions of azines and imines (including criss-cross cycloaddition) 76S349... 

Burger s criss-cross cycloaddition reaction of hexafluoracetone-azine (76S349) is also a synthetic method of the [CNN + CC] class. In turn, the azomethines thus produced, (625) and (626) (79LA133), can react with alkenes and alkynes to yield azapentalene derivatives (627) and (628), or isomerize to A -pyrazolines (629) which subsequently lose HCF3 to afford pyrazoles (630 Scheme 56) (82MI40401). 

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]... 

Because the criss-cross cycloaddition reaction is a sequence of two [3+2] cycloaddition steps, the reaction with a,co-diolefins offers a new entry into macro-molecular chemistry New types of polymers with interesting structures and prop erties can be synthesized [213, 214, 215] (equation 48)... 

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>. 

Some examples of the lateral cyclization of suitable O-allyl and O-propargyl derivatives were discussed in CHEC-11(1996) <1996CHEC-II(8)747>. Thermal reaction of silyl diazoacetate 303 in xylene provides unspecific decomposition and a minor amount (about 2%) of a colorless solid can be precipitated with ether. The X-ray diffraction analysis identified the structure 305, which is a product of the lateral criss-cross cycloaddition of primarily formed azine 304 (Scheme 43) <2000T4139>. 

Thermally induced intra-intermolecular criss-cross cycloaddition of nonsymmetrical azines 363 in the presence of phenyl isocyanate provides the corresponding products of the mixed criss-cross cycloaddition 364 (Scheme 55) <2002TL6431>. Two different reaction mechanisms, intra-intermolecular and inter-intramolecular, of the mixed criss-cross cycloaddition with opposite sequence of reaction steps are possible. Quantum chemistry calculations suggest the intra-intermolecular mechanism as the most probable mechanism of this reaction <2004CCC231>. 

A number of other ring systems have been prepared by intramolecular bis-annulation procedures. Pyrrolothiadiazolines 174 were prepared by condensation between hydrazides and compound 173 (Equation 14) <1998JPR676>. The thermally induced intra-intermolecular criss-cross cycloaddition of azine 175 in the presence of phenyl isocyanate leads to heterocyclic compound 176 containing three fused five-membered rings (Equation 15) <2002TL6431>. 

Formation of pyrazolo[l,2-a]pyrazoles via similar criss-cross cycloaddition has been reported (82LA845,82LA853) (Scheme 27). Synthesis of pyrazolo[l,2-a]pyrazoles with azines via criss-cross cycloaddition with electron-rich olefins has been reported [69JCS(D)816]. 

Rees and co-workers in their study of the reactions of trithiazyl trichloride in the preparations of heterocyclic compounds have noted that the isothiazolo[5,4-, isothiazole compound 140 was produced in low yield on reaction with conjugated dienes, along with the other heterocyclic systems 142-145 in much higher yields (Equation 28). Since it is known that trithiazyl trichloride is in thermal equilibrium with its monomer NSCl (Equation 29), the authors propose the so-called criss-cross cycloaddition reaction (Equation 30) which has been reported for azabu-tadienes, but this represents the first example of such a criss-cross cycloaddition to an all-carbon diene <1998CC1207>. 

Criss-cross cycloaddition of azines also involves two successive 1,3-dipolar cycloadditions (Scheme 8) (76S349). 

The formal criss-cross cycloaddition product of cyanogen with sulfur trioxide (molar ratio 1 2) has been shown to be l,2,3-oxathiazolo[5,4-d][l,2,3]oxathiazole 2,2,5,5-tetroxide (5). The S—O bond in the ring is extremely long at 1.71 A, while the exocyclic S=0 bonds are shortened to 1.39 A, suggesting a description of the molecule in terms of bond-nonbond resonance, the resonance formulae (5a) and (5b) also providing some rationalization for the short C—O bond (1.29 A) (79AG(E)223). 

Diazoacetic acid silyl esters can be prepared by fra t-esterification of tert-butyl diazoacetate with trialkylsilyl triflate <1985JOM33>. Analogously prepared (alkenyloxy)silyl 203 and (alkynyloxy)silyl diazoacetates 206 underwent silicon-tethered 1,3-dipolar cycloaddition reactions as shown in Scheme 37 and Equation (38). Compound 205 resulted from a lateral criss-cross cycloaddition of the intermediate azine 204, which was formed from two molecules of 203 by diazo + diazo or diazo + carbene reaction <2000T4139>. On the other hand, when silyl diazoacetates 206 were kept in xylene at 142 °C for 1 h, bicyclic pyrazoles 207 were obtained (Equation 38). 

Corrosion inhibitors, [1.2,4]triazino[4,3-ojbenzimidazoles, 59, 155 Coulson-Rushbrook theorem, 55, 273 Coumarins, see l-Benzopyran-2-ones Coupling reactions, trifluoromethyl iodide with aryl halides, 60, 12 Covalent hydration in 6-nitro-l 1,2,4]triazolo[ 1,5-a)-pyrimidines, 57, 107 of coordinated ligands, 58, 138 Creutz-Taube ion, 58, 124 Criss-cross cycloadditions, of... 

Both heterobicyclic compounds 8 and 13 readily undergo a base-induced [3-1-2] cycloelimination (Scheme 3) Upon treatment with potassium tert-butoxide at room temperature, the HNCY fragment of the triazolidine moiety of 8 (Y = S) and 13 (Y = O) is eliminated, thus reversing the second step of the criss-cross cycloaddition cf. Scheme 2). 

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. 

Nuyken [13] used a criss-cross cycloaddition to prepare the hard block of a copolymer (Scheme 10) followed by a polyaddition (Scheme 11). 

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