Azomethine imine intermediates

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,... 

The reaction of aldehydes with disubstituted hydrazines gives, via the addition product (380), the azomethine imine intermediate (381), which dimerizes to the hexasubstituted hexahydrotetrazine (377 Scheme 21). 

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... 

Lactones of azocarboxylic acids are remarkably reactive. In the presence of phenyl isocyanate, the imino isocyanate formed from reactive 2-hydrazono-A3-l,3,4-oxadiazolines via a 1,3-dipolar cycloreversion is intercepted to give [l,2,4]triazolo[l,2-a]-[l,2,4]triazole-l,3,5-triones by means of two subsequent [2 + 3] cycloadditions via azomethine imine intermediates (Scheme 10) (76T2685). 

The reaction of 151 with benzaldehyde dimethylacetal 157 proceeds in a similar fashion < 1999TL3727,2000S1170>. The resulting azomethine imine intermediate 158 reacts with the dipolarophilic diethyl acetylenedicarboxylate to give 159. When kept as an oil, the latter is oxidized rapidly in the presence of air to give pyrazole 160 (Scheme 23). 

The mechanisms of the cascade cyclizations of homoallenyl aldazines and analogues to afford tetracyclic compounds have been computed and double sequential crisscross 1,3-dipolar cycloaddition through azomethine imine intermediates has been characterized both for the homoallenyl aldazine and for its ketene analogue (Scheme 23). ... 

The thermal [l,4]-silatropic shift of the silyl group on to the oxygen atom of the nitroso group of Q -silylnitrosamines (171) to give an azomethine imine intermediate (172) has been reported. These intermediates have been shown to undergo 1,3-dipolar cycloadditions with dimethyl acetylenedicarboxylate to afford pyrazoles (173) see Scheme 42. 

Thermolysis of 6-substituted l,5-diazabicyclo[3.1.0]hexanes 326, easily available from 325, leads to a diaziridine ring opening and to the intermediate formation of labile azomethine imines 327. These compounds can be stabilized by a proton shift to form 1-substituted 2-pyrazolines 328. However, when the thermolysis is carried out in the presence of a 1,3-dipolarophile, the corresponding products of dipolar cycloaddition can be obtained. For example, iV-arylmaleimides provide mixtures of the major trans- and minor air-products 329 and 330, respectively (Scheme 47) C1999RJO110, 2001RJ0841, 2003RJ01338, 2004RJ067>. 

Addition of A-mesityl benzimidazolyl carbene 720 to an a,/3-unsaturated aldehyde generates a homoenolate intermediate that undergoes an addition/acylation sequence with azomethine imine 719 to afford (3R, 5S, 6S )-177-pyrazolo[l,2- ]pyridazine-l,8(5//)-diones 721 with excellent diastereoselectivity. Compound 721 (Ar = R = Ph) treated with sodium hydoxide in methanol or benzylamine provided nearly quantitatively, ring-opened products 722a and 722b, respectively (Scheme 116) <2007JA5334>. 

Although formally the product of 1,4-addition of the carbene to the ADC 4n unit, 1,3,4-oxadiazolines probably arise via initial nucleophilic attack of the diazo compound to give, after loss of N2, a dipolar intermediate. This intermediate azomethine imine can collapse directly to give the oxadiazoline,... 

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). 

Moore et a/.462 have studied cycloadditions to the 1,2-diazepinium betaines (1), which are also vinylogous azomethine imines. Ketenes and isocyanates add in a 1,5 manner and rearrange to 1,3-cycloadducts. Dimethyl acetylenedicarboxylate gave in 30 minutes 33% of 2, the formal product of a 1,3-cycloaddition, but possibly formed via a 1,5-cycloaddition. On heating, 2 gave 6 and another product via the postulated intermediates 4 and 7. Thermolysis of the related compounds 3 463 gave 5.464... 

Aldehyde (166) reacted with excess hydrazine hydrochloride to afford a pyrazoline in 63% yield a mixture of pyrazoline and pyrazolidine was obtained under an inert atmosphere.83 This reaction presumably involves the hydrazone and protonated azomethine imine as intermediates. Using (166) in excess afforded a bisintramolecular adduct in 87% yield. 

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 addition product of N- nitrosopyrrolidine with phenyllithium gives a compound which reacts with DMAD to give a pyrrolo[ 1,2-Z> ]pyrazole, possibly via an intermediate azomethine imine (equation 37) (73JOC4259). 

Azomethine imines have been postulated as intermediates in the reaction of aryl-substituted diazo compounds with N-phenyltriazolinedione (PTAD) and DMAD, leading to pyrazolo[l,2-a][l,2,4]triazoles (Scheme 11) (81TL2535). 

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... 

Treatment of oc-halo ketones 1392 (X = Br, Cl) with potassium thiocyanate and monosubstituted hydrazines 1393 provides Ar-aminoimidazoline-2-thiones [1397, R R = Me, Ph R R = (042)4 R = Ph, 4-O2NC6H4, PhCH2, etc.]. The reaction is considered to proceed via the formation of azo-alkenes 1394 and thiocyanic acid 1395. The intermediates, in turn, undergo a [34-2] cycloaddition reaction to give azomethine imine cycloadducts 1396, which proceed to the final products 1397 (Scheme 361) <199714(45)691, 2003JME1546>. 

Ninhydrin is allowed to react with a-amino acids in methanol at room temperature in the presence of N-phenylmaleimide to give stereoselective cycloadducts 104 in good yields, confirming the ylide intermediacy (84CC180). The N-unsubstituted azomethine ylide intermediates 103, when no dipolar-ophile is present, are transformed into a purple dye 106, called Ruhemann s purple, through a transamination into imine tautomers 105. This ninhydrin... 

With azobenzenes 661, vinylidene carbene, generated from silylvinyl triflate, gives tetrazoles 662 as a result of [3+2]-cycloaddition of the intermediate azomethine imines 663 to the N = N bond of a second azobenzene molecule (84JA6015). 

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