Imine carbon substituted

The procedure given here stems from our synthetic effort toward (+)-jasplakinolide9 11 that contains the p-amino acid (R)-p-tyrosine.12 This protocol permits the introduction of the desired carbon substituted at the p-site in an enantioselective manner. This approach contrasts with previous methodologies, which develop the chiral center via conjugate addition of an amine to an a,p-unsaturated system,13 reduction of a C=C or C=N functionality,14 or C-C bond formation involving imines and enolate derivatives.15... 

Ethyleneimine (aziridine) and carbon-substituted alkyleneimines are relatively weakly basic compounds [43, 44], This is ascribed to 71-electron delocalization in the ring [44]. By protonation of the imine cycle this aromaticity disappears, and iminium rings are much more readily broken than imines [45], Also the N-alkylethyleneimines are only weakly basic, and they are also more resistant to ring-opening nucleophilic reactions [46]. 

Furthermore, it is of interest to note that the overall process that leads to intermediates VI and VIII here are basically equivalent in the sense that both are the consequence of the attack by a nucleophilic entity at the imine carbon atom. However, while the introduction of alkoxy at this carbon is the equivalent of a Sn2 substitution, the introduction of hydride requires the more circuitous and conceptually different path of reductive addition followed by nonoxidative elimination. In consequence, the latter implies reduction, the former does not. 

The discovery that -imines obtained from a variety of isopropylidene protected sugar open-chain aldehydes and ketenes, or ketene equivalents afford cz5-substituted 8-lactam adducts usually with a high asymmetric induction and definite relative geometry depending on the absolute configuration of the stereogenic center next to the imine carbon atom (Scheme 1) [21-24], prompted many laboratories to exploit this reaction in a number of syntheses. Imines derived from both easily available enantiomeric forms of 2,3-0-isopropylidene-glyceraldehyde are particularly attractive. 

Part two (section 3) deals with the hydrosilylation of unsaturated carbon-heteroatom bond, mostly 0=0 and 0=N (but also C N, and C=S), as a catalytic method for the reduction of C=0 and C=N bonds—one of the most fundamental transformations in organic chemistry. Catalytic hydrosilylation of prochiral ketones and imines with substituted silanes and siloxanes that can provide (if followed by hydrolysis) convenient access to chiral alcohols and amines, respectively, discussed from the catalytic and synthetic point of view completes this part. 

Carbon—nitrogen double bonds in imines, hydrazones, oximes, nitrones, azines, and substituted diazomethanes can be cleaved, yielding mainly ketones, aldehydes and/or carboxyHc acids. Ozonation of acetylene gives primarily glyoxal. With substituted compounds, carboxyHc acids and dicarbonyl compounds are obtained for instance, stearoHc acid yields mainly azelaic acid, and a smaH amount of 9,10-diketostearic acid. 

Triaryl-substituted imines are converted to the corresponding nitrones by peroxyacetic add [87] (equation 79) substitution of one pentafluorophenyl group by a phenyl group at the carbon atom reduces the yield to ca. 20% [[Pg.349]

The reaction of tnfluoromethyl-substituted A -acyl umnes toward nucleophiles in many aspects parallels that of the parent polyfluoro ketones Heteronucleophiles and carbon nucleophiles, such as enarmnes [37, 38], enol ethers [38, 39, 40], hydrogen cyanide [34], tnmethylsilylcarbomlnle [2,47], alkynes [42], electron-nch heterocycles [43], 1,3-dicarbonyl compounds [44], organolithium compounds [45, 46, 47, 48], and Gngnard compounds [49,50], readily undergo hydroxyalkylation with hexafluoroace-tone and amidoalkylation with acyl imines denved from hexafluoroacetone... 

The reaction of tnfluoropymvates or their acyl imines with carbon nucleophiles offers a convenient route to a-tnfluornmethyl substituted a-hydroxy or a-ammn acids Reduction of the keto or immo function yields 3,3,3-tnfluorolac-tates or 3,3,3-tnfluoroaIanine esters [32]. 

Under acidic conditions, imine 12 is protonated to give the iminium ion 13 which undergoes an electrophilic aromatic substitution reaction to form the new carbon-carbon bond. Rapid loss of a proton and concomitant re-aromatization gives the tetrahydroisoquinoline 14. 

Polar C=Y double bonds (Y = NR, O, S) with electrophilic carbon have been added to suifinic acids under formation of sulfones. As in the preceding section one must distinguish between carbonyl groups and their derivatives on the one hand, and carboxylic acids (possessing leaving groups at the electrophilic carbon) on the other. Aldehydes " of sufficient reactivity—especially mono-substituted glyoxals - —and their aryl or arylsulfonyl imines have been added to suifinic acids (in a reversible equilibrium) to yield a-hydroxy or a-amino sulfones the latter could also be obtained from the former in the presence of primary amines (equation 26). 

Several functional groups containing carbon-nitrogen double bonds can participate in radical cyclizations. Among these are oxime ethers, imines, and hydrazones.337 Hydrazones and oximes are somewhat more reactive than imines, evidently because the adjacent substituents can stabilize the radical center at nitrogen.338 Cyclization at these functional groups leads to amino- substituted products. 

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