Cyclic azomethine imines

The above cycloaddition process consists of two separate [3-1-2] cycloaddition steps and represents a 1,3-2,4 addition of a multiple bond system to a hetero-1,3-diene [7S7]. The structure ot the azomethine imine intermediate has been proved unequivocally by X-ray analysis [195] Ethylene [194], acetylene [/iS2] . many alkyl- and aryl- as well sgemmal dialkyl- and diaryl-substituted alkenes [196,197, 198, 199], dienes [200], and alkynes [182, 201], certain cyclic alkenes [198, 199,... 

Chen extended the scope of his iminium ion catalysed [3+2] cycloaddition with azomethine imines (see Sect. 2.1.2) to encompass cyclic a,P-unsaturated ketone substrates using primary amine 147 as the catalyst [194]. Interestingly, the presence... 

Alkylidene-phosphapyrazolines 98-101 are much more thermally stable than their relatives 88, which do not possess the exo-methylene substitution. Dediazo-niation of 98 required heating in toluene at 110°C and gave one or more of the following products, probably via intermediate diphenylmethylene(vinylidene)phos-phoranes methylenephosphiranes, (2-siloxyvinyl)phosphanes, 2//-l,3-oxaphos-pholes, and l-alkylidene-2,3-dihydro-l//-benzo[c]phospholes (169). Thermolysis of 100 ( R = t-Bu, 1-adamantyl) afforded isolable 2-phosphabutadienes (169). The photochemical elimination of N2 from 98 generated cyclic azomethine imine dipoles 104 (Scheme 8.24), which rearrange to compounds 105 and 106 that could be further trapped with DMAD to form 107 (170). 

The azomethine imine (155), containing a cyclic dipolarophile, cyclized to a tetracyclic pyrazolidine in 48% yield.78 Aldehyde (156), containing a furan ring, reacted with A/-methyl-A/ -(phenylacetyl)hydra-zine to afford an azomethine imine the imine cyclized to one product, probably with the two new rings cis fused.80... 

The mesoionic compounds known as sydnones serve as cyclic azomethine imines. Thus, sydnone (167), isolable after preparation from die corresponding nitrosamine, underwent cyclization as an azomethine imine at 20-35 C (Scheme 52).86 Photolysis of sydnones also results in cyclization but through nitrile imine intermediates vide infra). 

The products derived from intermolecular cycloaddition of sydnones readily lose carbon dioxide. If the original cycloaddition is carried out on a diene, the resulting azomethine imine intermediate can be trapped intramolecularly. Thus, 1,5-cyclooctadiene cycloadded to a sydnone to afford the cycloadduct (168).78b It is theorized that the intermolecular monocycloadduct (169) was formed, lost carbon dioxide, and cycloadded as a cyclic azomethine imine to the remaining C—C double bond. Conjugated dienes have been shown to undergo a similar sequence.87... 

Sydnones can be regarded as cyclic azomethine imines and as such they undergo thermal cycloaddition reactions with a range of dipolarophiles. Thus, reaction with phenyl isocyanate converts 401 into 1,2,4-triazole 402. On photolysis, 3,4-diarylsydnones lose carbon dioxide and give nitrile imines, which can also be intercepted by dipolarophiles. Thermal reactions with acetylenic dipolarophiles lead to the formation of pyrazoles (Scheme 88) however, these reactions are rarely completely regioselective with unsymmetrical alkynes, e.g., <2000BKC761, 2000TL1687>. 

Professor Leonid Belen kii (Zelinsky Institute, Moscow) has rationalized the orientation of substitution in furan, thiophene, and pyrrole. Professor Joachim SchantI of University of Innsbruck (Austria) surveys the chemistry of cyclic azomethine imines derived from azo compounds, illustrating the diversity of their possible [3+2] cycloaddition reactions. 

Cyclic Azomethine Imines from Diazenes (Azo Compounds)... 

Cycloadditions of cyclic azomethine imines 44 and 45 with dimethyl acetylene-dicarboxylate... 

Cyclic azomethine imines 2,2-dimethyl-4-oxo-3,4-dihydro-2/-/-pyrrolium-l-anilide (70) and 3,3-dimethyl-5-oxo-l-phenyl-2,3,4,5-tetrahydropyridazin-l-ium-2-... 

This report covers two topics (1) The generation of 2-thioxo-2,4-dihydro-3fT-imidazol-l-ium-l-imides as intermediates in the course of [3+2] cycloaddition reactions of azoalkenes and thiocyanic acid resulting in the formation of l-aminoimidazole-2-thione derivatives some further reactions of these heterocycles are presented as well. (2) The rhodium-catalyzed intramolecular interaction of co-diazenyl a -diazo ketones giving rise to the formation of mostly two cyclic azomethine imine isomers with an exocyclic terminal nitrogen atom and with all three... 

INTRAMOLECULAR INTERACTION OF DIAZENE N-ATOMS WITH CARBENOID C-ATOMS. CYCLIC AZOMETHINE IMINES... 

Cyclic azomethine imines 2,3-dihydroazetium-l-anilinide (44) and 4,5-dihydro-lH-pyrazol-2-ium-l-ide (45)... 

Scheme 9 Rhodium(ll)-induced conversion of a-diazenyl-a -diazo ketone 42 [n = 0) into cyclic azomethine imines 44 and 45.

Scheme 11 Reaction of the four-membered cyclic azomethine imine 44 with DMAD.

A. S. Rettenbacher, "Stable Cyclic Azomethine Imines. Synthesis, Structure Elucidation, Reactions", Diploma Thesis, University of Innsbruck (1997). 

In theory, a pyrazole could react towards dienophiles or dipolarophiles as an azadiene (A) or as a 1,3-dipole of the azomethine imine category (B), both situations being identical with regard to the number of 7r-electrons involved (Figure 25) (see also Section 4.02.1.9.1). There is also the possibility that it may react as an alkene (C) or as an imine (D) towards dienes or 1,3-dipoles. In the case of ethenylpyrazoles a final possibility of a Diels-Alder reaction involving an exo- and endo-cyclic double bond must be considered. 

The authors have further screened the catalytic conditions, and satisfactory results for both enantioselectivity and yield were obtained by using a bulky acid, triisopropylbenzenesulfonic add (TIPBA), at higher temperature (40 °C). A variety of azomethine imines reacted directly with cyclic enones, forming the desired tricyclic products in good yield (72-99%) and ee (86-95%), while having excellent diastereos-electivity (all >99 1) (Table 10.9). Moreover, 6 -OH-9-amino-9-deoxyepi-quinidine lr... 

Table 10.9 Asymmetric 1,3-dipolar cycloaddition of cyclic enones and azomethine imines.

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