Diazoalkanes to imines

In the presence of metal catalysts such as Yb(OTf)3, diazoalkanes add to imines to... 

The addition of diazoalkanes to alkenes and alkynes has been shown to be a HOMOdiazoalkane-LUMOdipo,arophi,e controlled reaction,5153 and because the orbital energies of imines are comparable to those of electron-poor olefins, the reactivity of diazoalkanes toward imines may also be considered a HOMOdiazoalkane-LUMOimine favored interaction.338... 

An unusual course of thermolysis occurs in 5-amino- and 5-alkoxytri-azolines, which are formed only as intermediates in the reaction of enamines and enol ethers with azides bearing electron-withdrawing groups it involves cleavage of the N-l/N-2 as well as the C-4/C-5 bonds of the triazoline ring to yield diazoalkanes and imines with one fewer carbon than in the triazolines (amidines and imino ethers) (Scheme 144)233.250 272 431-433 in a cycloelimination reaction, the reverse of diazoalkane-imine cycloaddition. The intermediate formation of a diazonium zwitterion is suggested,233,247 but whether the thermolysis occurs in a one- or two-step reaction is not established. 

Stanovnik B, Jelen B, Turk C, Zlicar M, Svete J (1998) 1,3-dipolar cycloadditions of diazoalkanes to pyridazines. Asymmetric 1,3-dipolar cycloaddition of azomethine imines derived from diazoalkane-pyridazine cycloadducts. J Heterocycl Chem 35 1187-1204... 

While the electrocyclic ring-opening of aziridines to azomethine ylides is well known, the reverse reaction has also been studied as a route to aziridines . This process is implicit in the cis-trans equilibration of substituted aziridines <67JA1753, 7UA1779), and may be involved in the reaction of diazoalkanes with imines <84T2569>. Convincing evidence for the electrocyclization of... 

Reactions offluorinated dipoles. In recent years, much effort has been devoted to the preparation of tnfluoromethyl-substituted 1,3-dipoles with the goal of using them to introduce trifluoromethyl groups into five-membered nng heterocycles Fluorinated diazoalkanes were the first such 1,3-dipoles to be prepared and used in synthesis A number of reports of cycloadditions of mono- and bis(tnfluo-romethyl)diazomethane appeared prior to 1972 [9] Other types of fluonne-substi-tuted 1,3-dipoles were virtually unknown until only recently However, largely because of the efforts of Tanaka s group, a broad knowledge of the chemistry of tnfluoromethyl-substituted nitrile oxides, nitnle imines, nitnle ylides, and nitrones has been accumulated recently... 

An alternative preparation of aziridines reacts an alkene with iodine and chloramine-T (see p. 1056) generating the corresponding A-tosyl aziridine. Bromamine-T (TsNBr Na ) has been used in a similar manner." Diazoalkanes react with imines to give aziridines." Another useful reagent is NsN=IPh, which reacts with alkenes in the presence of rhodium compounds or Cu(OTf)2 to give N—Ns aziridines. Manganese salen catalysts have also been used with this reagent. ... 

These complexes can be isolated in some cases in others they are generated in situ from appropriate precursors, of which diazo compounds are among the most important. These compounds, including CH2N2 and other diazoalkanes, react with metals or metal salts (copper, palladium, and rhodium are most commonly used) to give the carbene complexes that add CRR to double bonds. Ethyl a-diazoacetate reacts with styrene in the presence of bis(ferrocenyl) bis(imine), for example, to give ethyl 2-phenylcyclopropane-l-carboxylate. Optically active complexes have... 

Alkylidene sulfenes (75), generally prepared by the dehydrohalogenation of alkylsulfonyl chlorides, add readily to electron-rich multiple bonds. For example, with enamines, the thietane dioxide (e.g., 76) is formed diazoalkanes yield thiirane dioxides (episulfones) and imines (Schiff bases) afford 1,2-thiazetidine 1,1-dioxides. There are available numerous reviews of sulfenes, including cycloaddition reactions.102... 

Cyclohexadiene 45 was converted to 46 by what has proven to be a general method for preparation of the cyclohexa-2,4-dien-l-one ring system.2 Fragmentation of the aziridinyl imine in 46 at 110 °C gave an intermediate diazoalkane which underwent an intramolecular 1,3-dipolar cycloaddition to give the pyrazoline 47. At 140 °C, pyrazoline 47 expelled N2 and rearranged to the tricyclic ketone 48. The development of this and related bicyclizations29 illustrated a practical synthetic equivalence of an intramolecular diene-carbene 4-1-1 cycloaddition in the cyclohexa-2,4-dien-l-one series. 

Stanovnik and co-workers (100,101) systematically investigated the cycloaddition reactions of diazoalkanes with unsaturated nitrogen heterocycles, such as azolo-[l,5-fl]pyridines, pyridazin-3(2/7)-ones, and [fo]-fused azolo- and azinopyridazines. The Stanovnik group have studied the further transformations of the products and reviews of this chemistry are available. In a typical example, the reaction of 6-chlorotetrazolo[l,5-/7]pyridazine (37) with 2-diazopropane yields the NH,NH-dihy-dro-pyrazolo[4,3-(i]tetrazolo[l,5-/7]pyridazine 38 (102) (Scheme 8.11). The latter substrate reacts with acetone to produce an azomethine imine 39 that thermally rearranges to give the fused dihydro-1,2-diazepine 40. The azomethine imine obtained with glucose can be trapped with methyl acrylate to furnish the C-nucleoside 41 (103). 

The characteristics of the 1,3-dipolar cycloaddition mechanism of azides and other 1,3-dipoles (such as diazoalkanes, azo-methine imines, nitrones, nitrile imines, nitrile oxides) have been described in detail by Huisgen.191 19 According to the author, the addition of a 1,3-dipole (a b c) to a dipolarophile (d e) occurs by a concerted mechanism in which the two new a bonds are formed simultaneously although not necessarily at equal rates (32). As a consequence, a stereoselective cis addition is observed. Thus, the addition of p-methoxyphenyl azide to dimethyl fiynarate (33) yields l-(p-methoxyphenyl)-4,5-froiw-dicarbomethoxy-AMriazoline (34),194 and 4-nitrophenyl azide gives exclusively the respective cis-addition products 35 and 36 on addition to irons- and cis-propenyl propyl ether.196... 

Perfluoroalkyl-substituted nitriles react readily with various 1,3 dipoles, such as azomethine ylides [755,156,157],azometlune imines [158],diazoalkanes [759],azides [160 161,162], and nitrile ylides [163] to give stable five-membered ring systems (equation 37)... 

There are two main approaches to the synthesis of A2-l,2,3-triazolines these involve the union of the C—C and N—N—N fragments as in the olefin-azide additions or alternately building from the C—N and C—N—N moieties as achieved through the imine-diazoalkane reactions (Scheme 2). The choice is determined by the type of substitution desired on the triazoline ring. Imines in general can be more easily prepared than the corresponding olefins. 

Diazoalkanes, like azides, are 1,3-dipoles of the propargyl-allenyl type (Scheme 87)15 and their reaction with imines provides a route for building the triazoline framework from the C—N—N and C—N fragments. Although diazomethane addition to the carbon-carbon double bond was achieved by von Pechmann in 1898,325 its reaction toward the carbon-nitrogen double bond was investigated only 50 years later. 

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