Imine compounds selectivity

Increasing interest is expressed in diastereoselective addition of organometallic reagents to the ON bond of chiral imines or their derivatives, as well as chiral catalyst-facilitated enantioselective addition of nucleophiles to pro-chiral imines.98 The imines frequently selected for investigation include N-masked imines such as oxime ethers, sulfenimines, and /V-trimcthylsilylimines (150-153). A variety of chiral modifiers, including chiral boron compounds, chiral diols, chiral hydroxy acids, A-sull onyl amino acids, and /V-sulfonyl amido alcohols 141-149, have been evaluated for their efficiency in enantioselective allylboration reactions.680... 

In the presence of excess monoalkylamine, carbonyl compounds in aqueous solution are in equilibrium with the corresponding imine. In most cases these imines cannot be isolated but they are reduced at a less negative potential than the carbonyl compound. Selective reduction of such equilibrium mixtures is a useful route to alkylamines from ketones in yields of 70-90%. The process fails with hindered ketones such as camphor and with bulky amines such as fert.-butyl amine. Overall the reaction has advantages of lower costs and simpler work-up compared to the use of cyanoborohydride reducing agents. In the electrochemical reaction, protonation of carbanion intermediates occurs from the more hindered side and where two isomeric products are fomied, the least hindered amine predominates [193]. 

The first compound selected for this study was the azadiene 1. Previous studies demonstrated that tetraphenyl-substitution in positions 3 and 5 of the P,y-unsaturated s) tem promotes efficient DPM, ODPM, and 1-ADPM reactions in acyclic 1,4-dienes," P,y-unsaturated aldehydes, and l-aza-1,4-dienes, respectively. Based on these precedents, the 2-azadiene 1 was considered to be a suitable candidate to undergo rearrangement of the di-7l-methane type. Triplet-sensitized irradiation of azadiene 1, using acetophenone, for 25 min, afforded two new products that were identified as the cyclopropyl imine 2 (11%) and the vinylaziridine 3 (3%) (Scheme 1). Compound 2 hydrolyzes to the corresponding cyclopropyl amine during isolation. ... 

The results obtained in the SET-sensitized irradiation of 2-aza-1,4-dienes using DCA as an electron-acceptor sensitizer suggested that other P,y-unsaturated compounds could also participate in di-Jt-methane type rearrangements via radical-cation intermediates. To test this proposal, we have carried out a study on a series of l-substituted-l-aza-l,4-dienes. The compounds selected for this study were the P,y-unsaturated imines 39a, 39b, and 40a. DCA-sensitized irradiation of these imines in acetonitrile, using biphenyl as co-sensitizer, yielded the corresponding cyclopropyl imines 41a, 41b, and 42a, which hydrolyze to the corresponding cyclopropane carbaldehydes during isolation. ... 

Other advances include the construction of seven- and nine-membered rings via the analogous [4-1-3] and [6-1-3] cycloadditions with dienes and trienes respectively. Heterocycles, such as tetrahydrofurans and pyrrolidines, are accessible using carbonyl compounds and imines as substrates. The following discussion is organized around these recent discoveries. It serves to illustrate the versatility and the high degree of selectivity which are some of the distinctive features of the Pd-TMM chemistry. 

The diastereoselectivity of the addition of metalated croty] compounds 1 to the imine moiety has been constantly improved by changing the metal from magnesium over lithium, zinc, aluminum to boron and tin113 (see Table 7). With the latter a high selectivity in favor of the. vj M-product 3 was achieved. The unh-diastereomer 4 results exclusively from addition of boron reagents to A-arylimines 21. 

H(65)1889, 2005EJO3553>. Starting dihydro[l,2,4]triazolo[3, 4-4]benzo[l,2,4]triazines 482 readily react with aromatic aldehydes to yield iminium salts 483. These salts treated with a base (e.g., triethylamine) are deprotonated to reactive 1,3-dipolar azomethine imines 484. In contrast to related five-membered heterocycles, these compounds are relatively unstable on storage in the solid form and particularly in solution. Fortunately, this obstacle can be easily circumvented by their in situ preparation and subsequent 1,3-dipolar cycloaddition. These compounds can participate in 1,3-dipolar cycloadditions with both symmetric and nonsymmetric dipolarophiles to give the expected 1,3-cycloadducts in stereoselective manner. Selected examples are given in Scheme 82. 

The mercuration of ferrocenylimines with Hg(OAc)2 has been studied. - 6 Mercuration occurs selectively at the a-position relative to the imine group to afford compounds 86a-i (Scheme gy107,108 The regioselectivity of these reactions points to the directing role of the Lewis-basic imine functionality. Similar factors probably play a role in the formation of the ferrocenylketone and ferrocenylaldehyde derivatives 87a-f and 87g-j, respectively. These derivatives readily react with amines to afford the corresponding imines (Scheme 9). Presumably, the Lewis-acidic mercury center of the monomercurated ferrocenylketones and ferrocenylaldehydes activates the carbonyl functionality toward nucleophilic attack by the amine. 

Itsuno et al.68c found that among the imines 150-153, TV-trimethylsilylimine derivative 153a has the highest reactivity. When it is treated with /i-allylox-azaborolidine 156, a compound derived from toluenesulfonyl norephedrine 155, a product with high selectivity (92% ee) is obtained. Scheme 3-53 depicts the... 

Amino alcohols.1 The reagent reacts with a typical imine such as N-benz-ylbenzenimine to form a product that is hydrolyzed to benzylphenylamine. The precursor is presumably a metallaaziridine, which is cleaved by electrophiles with insertion into the carbon-metal bond. Reaction of the intermediate (a) with a carbonyl compound results in a 2-amino alcohol after hydrolysis with moderate anfi-selectivity. 

Selected examples of the Michael-type addition of activated methylene compounds with imines... 

Aldehydes and ketones can be hy-drodimerized to pinacols (Eq. 2) [34-37]. With aromatic carbonyl compounds, the yields and selectivities are mostly higher than with aliphatic ones. The reaction has been extended to imines (Eq. 2, X = NAr, N-Bn) [38-41] and to heterohydrodimerizations affording, for example, y-lactones (Eq. 3) [42-44]. 

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