IV-Substituted imines

While hydrosilylation of imines is known to be effected by rhodium catalysts3, nickel catalysts prepared in situ from Ni(0Ac)2 4H20 and thiosemicarbazones are also found to promote the reactions of iV-substituted imines with HSiEt3 in dry DMSO at 35 °C, giving the corresponding secondary amines in excellent yields after basic work-up (equation 77)185. 

Coupling reactions. Conversion of oxime ethers to iV-substituted imines involving N—O to N—C bond exchange is empowered by CuTC. Organostannanes and organoboronic acids can supply the substituent. ... 

Tetrahydropyridinium methy lides, for example, 209, have been prepared in situ from the organotin- or organosilyl-substituted imines. These react with iV-phcnylmalcimidcs to produce the completely saturated pyrroloindolizines <1997TL5441, 2004JOC1919> (Equation 25). 

Binol-derived phosphoroamidite PipPhos (19) has been successfully used as a ligand for the Ir-catalyzed asymmetric hydrogenation of 2- and 2,6-substituted quinolines [39], 2- and 2,6-substituted quinoxalines [40], and IV-aryl imines [41] (Fig. 16). 

Imines formed from ammonia and aldehydes (RCH=NH) are very unstable and readily polymerize (Section 16-4C). However, substitution of an alkyl or aryl group on the nitrogen increases the stability, and IV-substituted... 

Scheme 67 [2+2] Cyclocarbonylation of allyl bromide with IV-a-aza-heteroaryl substituted imines...

In contrast, the Hoveyda and Snapper groups reported the efficient catalysis of silver acetate complexes of imine 204.86 These authors first established the superior performance of IV-ort/zo-methoxyaniline-substituted imines in the reaction with Danishefsky diene 195. Because of the modular nature of ligand 206, optimization of its structure could be achieved by surveying a combinatorial library of amino acid derivatives. The /-isoleucine para-methoxyaniline conjugate 206 proved the best. This ligand facilitated full conversion within 2-3 h with high yield and enantioselectivity (Scheme 2.53). 

It has been reported that amines (32JCS1142) or imines (53JCS143), when reacted with formaldehyde and hydrogen sulfide, give rise to iV-substituted 1,3-thiazetidines. However, in at least one case the structure was established to be an eight-membered ring dimer, which calls into question the structure of these compounds. 

Mono-alkyl-fnrans nndergo Mannich substitution under normal conditions," bnt fnran itself reqnires a preformed imininm salt for 2-substitution." iV-Tosyl-imines, generated in situ from iV-snlhnyl-p-tolnenesnlfonamide and aldehydes, bring about tosylaminoalkylation at C-2." The use of furan boronic acids allows Mannich snbstitntions at both a- and P-positions, with primary or secondary amine components." " ... 

The reduction of iV-diphenylphosphinyl imines of substituted cycloalkanones with lithium tri-sw-butylborohydride (L-Selectride) provides highly diastereoselective conversions to protected axial primary amines in 83-96% yield17. The reduction of cyclohexylidene diphenylphos-phinyl imines with sodium borohydride is less diastereoselective17. 

In iV-substituted N-imines, the negative charge can often be delocalized in the exocyclic substituent. This can be shown by the example of an N-acylimine by means of the mesomeric structures 79 and 80. The case is analogous to other iV-substituted Ar-imines. This possibility of delocalization is a significant difference between N-oxides and substituted N-imines. 

Hydroperoxides (/-butyl hydroperoxide, cumyl hydroperoxide, and hydrogen peroxide) add to the azomethine bond of pyridine iV-aryl-imines.138 The primary addition product reacts as indicated in Eq. (13) and leads to 1,6-dihydropyridazine derivatives (97). Unsymmetrically substituted iV-arylimines furnish two products the structure of the hydroperoxide has no influence upon the nature of the final product. 

Anodic oxidation of iV,AT-disubstituted trifluoroetbaiiimidamines 26 in dry acetonitrile gives iV-substituted 2-(trifluoromethyl)benzimi-dazoles 27 as shown in Scheme 22. °° ° Electron-donating para-substituents in the iV,lV -diaryl derivatives markedly promote this cyclization process, whereas -alkyl derivatives react to form p-ben-zoquinone imine derivatives 28 under the anodic oxidation conditions. 

Because a different stereochemistry for the aza-MBH reaction involving different Michael acceptors was observed, in a continuation of our work, we reinvestigated systematically the reaction of iV-sulfonated imines with various activated olefins, including ethyl vinyl ketone (EVK), acrolein, phenyl acrylate and a-naphthyl acrylate. An interesting inversion of absolute configuration between the adducts derived from MVK or EVK and those from acrolein, methyl acrylate, phenyl acrylate or a-naphthyl acrylate was observed, indicating that the substitution patterns of the olefin may alter or even invert this trend.Similar to the addition to HFIPA, the (3-ICD-mediated addition of methyl, phenyl and naphthyl acrylates 149 to V-sulfonyl imines afforded adducts 150 with an (5) configuration, which is opposite to that observed with aldehydes (Scheme 2.71). ... 

Thiourea-catalysed Maunich reactions of 3-substituted oxindoles with iV-Boc imines. 

Interestingly, an unsymmetrical bifunctional protonated catalyst was developed by Johnston and Singh to promote the asymmetric aza-Henry reaction of a-alkyl a-nitroesters with iV-Boc imines, providing the corresponding chiral a-substituted syra-a,p-diamino acid derivatives of phenyl alanine in high yields, excellent enantioselectivities of up to 99% ee and moderate to high diastereoselectivities of up to 90% de, as shown in Scheme 3.27. ... 

Reactions with Imines. In some cases, BSF can react with imines to provide AA -acetal derivatives. For example, treatment of the quinone methide-substituted imine 3 (R = t-Bu, X = OAc, formed via lead(IV) oxide-mediated oxidation of Schiff base 2) provides the corresponding iV-formyl-lV-imino-lV,)V-acetal 4, with concurrent rearomatization of the quinone unit (eq 13). However, when this procedure was adapted for multigram scale, the yield of desired product was very low, with 9% epimer formation. Changing of the oxidant to DDQ allowed smoother reactions... 

In some cases, less activated iV-aryl imines were transformed into the corresponding trifluoromethylamines by reaction with TMSCF3 in the presence of CsF and TMS-imidazole, or with fluoride initiators such as TBAT or TMAF (eq 14). However, in the latter example higher amounts of fluoride caused the loss of HF and therefore difluoromethylamines were obtained after reduction with NaBH4. When a stoichiometric amount of TMAF was employed, tetramethylammonium amides were formed and further treated with a variety of electrophiles to produce N-substituted trifluoromethylamines. IV-Methyl imines derived from salicyl-aldehydes reacted with TMSCF3 after forming an iminium cation (eq 15). 

Kobayashi et al. have also applied their chiral coordinative calcium catalysts successfully to asymmetric addition of malonates to imines, and the desired products were obtained in high yields with moderate to good enantioselectivities (Table 25) [97]. Several aromatic IV-Boc-imines bearing electron-withdrawing or donating groups were surveyed, and the enantioselectivities were around 70 % ees (entries 1-13). Unfortunately, an alkyl-substituted imine did not work well (entry 14). 

Arylnitrones react with diphenylketene to give [3+2] cycloadducts, which lose carbon dioxide to give ortho-substituted imines . From pyridine IV-oxide and diphenylketeneor dichloroketenesimilar reactions are observed. 

A novel domino annulation involving sulfur ylides (873) and salicyl iV-thiophosphinyl imines (872) has been developed in synthesis of a highly substituted traM5-2,3-dihydrobenzofurans (874) in high yields and excellent chemo- and stereoselectivities (Scheme 220). ... 

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