Imines intermolecular

Enamines derived from ketones are allylated[79]. The intramolecular asymmetric allylation (chirality transfer) of cyclohexanone via its 5-proline ally ester enamine 120 proceeds to give o-allylcyclohexanone (121) with 98% ee[80,8l]. Low ee was observed in intermolecular allylation. Similarly, the asymmetric allylation of imines and hydrazones of aldehydes and ketones has been carried out[82]. 

The tertiary amine is formed in a similar manner from the imine and a secondary amine. This side reaction can be minimized by carrying out the hydrogenation in the presence of ammonia, which tends to shift the equiHbrium back towards the imine. When a compound with two or more nitrile groups is hydrogenated, the formation of both cycHc and acycHc secondary and tertiary amines is possible, depending on whether the side reaction is intramolecular or intermolecular. For example, for the hydrogenation of adiponitfile ... 

The mechanism for the formation of ( )-169 is explained in terms of an intermolecular nucleophilic dimerization. Nucleophilic addition of C-3 of 19 to the 3 position of the initially generated cation 168 gives an imine-nitrone... 

By an analogous route, the cyclization of chiral (z-amino imines 197, bearing the proper tw-functionality in the o -alkyl chain, will lead to 3-substituted 1,2-diaminocycloalkanes 198. The intermolecular and intramolecular addition of allylic silicon and tin compounds to a-amino azomethine compounds should also be investigated. 

In 1992, Bergman et al. reported that zirconium bisamides Cp2Zr(NHR)2 catalyze the intermolecular hydroamination of alkynes with sterically hindered primary amines to give enamines or their tautomeric imines (e.g., Eq. 4.77) [126]. 

In a recent publication, Perumal and coworkers [441] described the condensation of an aldehyde 2-863 with an aniline 2-864 to give an imine which is trapped by a dienophile. However, when using this approach an intermolecular cycloaddition takes place as the reaction is performed as a three-component process using enol ethers or cyclopentadiene as dienophiles (Scheme 2.192). When using enol ether 2-... 

Intermolecular hydroamination of 1-alkynes with anilines has recently been performed using [Rh(COD)2]+ in combination with three equivalents of tricyclohexylphosphine (1.5 mol. % catalyst) at 50 °C to yield the corresponding imines (Equation (16)) 172... 

This chapter deals with [2 + 2]cycloadditions of various chromophors to an olefinic double bond with formation of a four-membered ring, with reactions proceeding as well in an intermolecular as in an intramolecular pattern. Due to the variety of the starting materials available (ketones, enones, olefins, imines, thioketones, etc.. . .), due to the diversity of products obtained, and last but not least, due to the fact that cyclobutanes and oxetanes are not accessible by such a simple one-step transformation in a non-photo-chemical reaction, the [2+2]photocycloaddition has become equivalent to the (thermal) Diels-Alder reaction in importance as for ring construction in organic synthesis. 

I.3.4.2. Intermolecular Cycloaddition at C=X or X=Y Bonds Cycloaddition reactions of nitrile oxides to double bonds containing heteroatoms are well documented. In particular, there are several reviews concerning problems both of general (289) and individual aspects. They cover reactions of nitrile oxides with cumulene structures (290), stereo- and regiocontrol of 1,3-dipolar cycloadditions of imines and nitrile oxides by metal ions (291), cycloaddition reactions of o-benzoquinones (292, 293) and aromatic seleno aldehydes as dipolarophiles in reactions with nitrile oxides (294). 

Ytterbium triflate [Yb(OTf)3] combined with TMSG1 or TMSOTf are excellent reagents for the conversion of a-methyl styrene and tosyl-imines into homoallylic amides 32 (Equation (19)) (TMS = trimethylsilyl).29 These conditions produce the first examples of intermolecular imino-ene reactions with less reactive imines. Typically, glyoxalate imines are necessary. A comprehensive examination of the lanthanoid metal triflates was done and the activity was shown to directly correlate with the oxophilicity scale. The first report used preformed imines, and subsequently it was found that a three-component coupling reaction could be effected, bypassing the isolation of the intermediate imine.30 Particularly noteworthy was the successful participation of aliphatic aldehydes to yield homoallylic amines. 

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 intermolecular reaction of imines with acceptor-substituted carbene complexes generally leads to the formation of azomethine ylides. These can undergo several types of transformation, such as ring closure to aziridines [1242-1245], 1,3-dipolar cycloadditions [1133,1243,1246-1248], or different types of rearrangement (Figure 4.9). 

Recently, intermolecular hydrophosphination of alkynes was also reported with ytterbium-imine complex catalyst precursors [20]. Aromatic alkynes react at room temperature to afford ( )-isomers, while aliphatic ones require heating at 80 °C and, quite surprisingly, (Z)-isomers (trans-addition products) are formed preferentially (Table 4). In this respect the ytterbium-catalyzed reactions are different from the radical process, in which the ( )-isomer formed initially isomerizes to the (Z)-isomer. 

Variously substituted nitrile imines are easily available and react readily with a wide range of double and triple bonds. Intermolecular cycloaddition is therefore an area of major interest, and a large proportion of the papers on the use of nitrile ylides in synthesis is concerned with the exploitation of this reaction. Space limitation means, regrettably, that work leading to results that were predictable on the basis of known chemistry (19) has generally not been included. 

Optically active chiral vicinal diamines are produced by Sml2-promoted reductive coupling of an imine derived from benzaldehyde and l-isopropyl-2-methoxyethylamine. Intermolecular coupling proceeds in a diastereoselective... 

Alkene hydroamination has been known for many years, but has been little used as a method in organic synthesis. Tobin Marks of Northwestern recently published a series of three papers that will make this transformation much mote readily accessible. In the first (J. Am. Chem. Soc. 125 12584,2003) he describes the use of a family of lanthanide-derived catalysts for intermolecular hydroamination of alkynes (to make imines, not illustrated) and alkenes. With aliphatic amines, the branched (Markownikov) product is observed, 1 — 2. With styrenes, the linear product is formed. When two alkenes are present, the reaction can proceed (3 —> 4) to form a ring, with impressive regioselectivity. 

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