Cycloaddition reactions with imines

Thiocarbamoyl isoselenocyanates 43 also undergo the [2+2] cycloaddition reaction with imines to give 1,3-selenazetidines 44. ... 

Vinylidene complexes of manganese and rhenium, generated in situ, undergo [2+2] cycloaddition reactions with imines to form 52. ... 

Dipolar cycloaddition reactions with azides, imines, and nitrile oxides afford synthetic routes to nitrogen-containing heterocycles (25—30). 

Thiatriazolin-5-imines undergo a variety of cycloaddition reactions with the elimination of Nt. 1,3-Dithiolylium-4-olates undergo cycloaddition reactions, e.g. as in Scheme 36 80AHC(27)i5l). Scheme 37 gives an example of cycloaddition in the oxathiazole series. 

Abstract The photoinduced reactions of metal carbene complexes, particularly Group 6 Fischer carbenes, are comprehensively presented in this chapter with a complete listing of published examples. A majority of these processes involve CO insertion to produce species that have ketene-like reactivity. Cyclo addition reactions presented include reaction with imines to form /1-lactams, with alkenes to form cyclobutanones, with aldehydes to form /1-lactones, and with azoarenes to form diazetidinones. Photoinduced benzannulation processes are included. Reactions involving nucleophilic attack to form esters, amino acids, peptides, allenes, acylated arenes, and aza-Cope rearrangement products are detailed. A number of photoinduced reactions of carbenes do not involve CO insertion. These include reactions with sulfur ylides and sulfilimines, cyclopropanation, 1,3-dipolar cycloadditions, and acyl migrations. 

Cyclopropyl ketones 32 and cyclopropyl imines 33 can also undergo [3+2] cycloaddition reactions with enones 34 in presence of NHC-Ni complexes to afford the corresponding cyclopentane compounds 35 (Scheme 5.9) [11]. The catalytic system is prepared in situ from the use of [Ni(COD),], SIPr HCl salt and KOBu, the reaction also required the use of Ti(O Bu) as an additive to improve yields and increase reactions rates. In most of the cases, th products 35 were obtained in good to excellent diastereoselectivities. 

In addition to undergoing cycloaddition reactions with alkenes and al-kynes, silenes readily undergo cycloaddition reactions with heteroatom multiple bonds such as C=0 and C=N, most commonly when the trapping reagent for the silene is either an aldehyde, ketone, or imine. In many... 

Reversible pyridine dissociation yields the non-Lewis base stabilized imido complex [Cp(NHAr) Ti=NAr] (54). This coordinatively unsaturated species undergoes a [2 + 2] cycloaddition reaction with allene to give an azatitanocyclobutane (55), which is then protonated to the /mamido complex. Elimination of enamine occurs followed by isomerization to the energetically more favorable imine. 

Electron-rich 6-[(dimethyl(amino)methylene)amino uracil 82 underwent [4+2] cycloaddition reactions with various in situ generated glyoxylate imine and imine oxides to afford novel pyrinhdo[4,5-J]pyrimicline derivatives 83-84 after elimination of dimethylamine from the (1 1) cycloadducts and oxidative aromatization. This one-pot procedure yielded excellent yields when carried out in the solid state and under microwave irradiation <06BMCL3537>. 

Cyclopropyl imines can be used as five-atom components in intermolecular [5 + 2]-cycloaddition reactions with dimethylacetylene dicarboxylate (DMAD) (Scheme 14).45 In this hetero-[5 + 2]-cycloaddition reaction, dihydroaze-pines are constructed from simple, readily available starting materials. The cyclopropyl imines can be preformed or made in situ by the condensation of cyclopropyl carboxaldehydes and amines. Although, thus far, DMAD is the only... 

The reaction of phenylazoalkenes 424 with an excess of potassium thiocyanate in acetic acid produces the cycloadducts 425 that undergo further [3+2]-cycloaddition reaction with thiocyanic acid at the azomethine imine function giving rise to the bicyclic product imidazo[l,5-3][triazole]-2,5-dithiones 41 (Equation 87) <1998SL786>. 

Dihydrodiazepines have been shown to undergo regioselective cycloaddition reactions with nitrile oxides or nitrile imines (88MI1 89JHC1619). 

The use of lithium amides to metalate the a-position of the N-substituent of imines generates 2-azaallyl anions, typically stabilized by two or three aryl groups (Scheme 11.2) (48-62), a process pioneered by Kauffmann in 1970 (49). Although these reactive anionic species may be regarded as N-lithiated azomethine ylides if the lithium metal is covalently bonded to the imine nitrogen, they have consistently been discussed as 2-azaallyl anions. Their cyclization reactions are characterized by their enhanced reactivity toward relatively unactivated alkenes such as ethene, styrenes, stilbenes, acenaphtylene, 1,3-butadienes, diphenylacetylene, and related derivatives. Accordingly, these cycloaddition reactions are called anionic [3+2] cycloadditions. Reactions with the electron-poor alkenes are rare (54,57). Such reactivity makes a striking contrast with that of N-metalated azomethine ylides, which will be discussed below (Section 11.1.4). 

Monosubstituted-5(4//)-oxazolones behave differently upon reaction with imines. Here, 4-methyl-2-phenyl-5(4/7)-oxazolone 196 (Ri = Ph, R2 = Me) reacts with imines derived from 2-furancarboxaldehyde or 2-thiophenecarboxaldehyde to give 3-amino-p-lactams 197. On the other hand, 196 reacts with chlorosul-fonyl isocyanate in a [2 + 2] cycloaddition to give dioxazabicycloheptanones 198 as shown in Scheme 7.60. ... 

Reactions with imines also occur under similar conditions leading to the formation of difluorinated /1-lactams [196,197]. Formally, this reaction corresponds to a [2+ 2]-cycloaddition across an imine there is also an isolated report of a difluoroketene reaction, shown in Eq. (63) [198]. Useful chemistry of a silyl difluoroketene acetal was reported recently Eq. (64) shows the efficient asymmetric reaction between this reactive carbon nucleophile and aldehydes catalysed by chiral Lewis acids [199]. 

Deshmukh et al. [134] have investigated the use of D-(+)-glucose derived chiral ketenes in the stereoselective synthesis of spiro-(3-lactams 226-227. The D-(+)-glucose acid chloride 224, serving as a ketene precursor, in the Staudinger cycloaddition reaction with appropriate imines 225 afforded the diastereomeric mixture of spirocyclic-(3-lactams 226-227 in 70 30 ratio, respectively. This reaction has cleanly produced only two diastereoisomers instead of theoretically possible four... 

Rink resin derived imines have been reported to give cycloaddition reactions with acetyl chlorides (or equivalent) using triethylamine as the base and dichloro-methane as the solvent at temperature ranging from 0°C to room temperature [70], The resin-bound p-lactam could be cleaved by using 50% trifluoroacetic acid (TFA) in dichloromethane, to afford the /V-unsubstituted p-lactam. 

An interesting [3 + 2] cycloaddition reaction, of imines with TMS allyl esters catalyzed by Pd complexes, has been developed and produces pyrrolidine rings in good to excellent yields under mild conditions (equation 170)611. 

Aromatic-substituted imines, especially those having electron-donating groups in the /wzz-position, undergo a [2+2] cycloaddition reaction with aryl isocyanates <1969CB938, 1978T101>. In the presence of an excess of azomethine, the six-membered triazine derivative is the exclusive product <1970MI149>. 

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>. 

Nowadays, it is an accepted mechanistic model [5, 6] that the photolysis step (which proceeds under thermo-reversible CO insertion) leads to species best described as chromium ketene complexes of type 7 (Scheme 2). Indeed, these intermediates exhibit a ketene-like reactivity they undergo [2 + 2] cycloaddition reactions with olefins, imines and enol ethers, whereas reaction with nucleophiles leads to carboxylic acid derivatives. 

Numerous [3 + 2] cycloaddition reactions have been performed with bis(trifluoromethyl)-substituted azomethine imines (79CB2609,79LAI33). Noteworthy is the [3 + 2] cycloaddition reaction with tetracyanoethylene, which adds across one of the nitrile functions instead of adding across the CC double bond. This is one of the rare examples of this type of periselectivity found in the case of tetracyanoethylene in [3 + 2] cycloaddition processes (76LA30). 

---