1,2-Diamines reactions with iminium salts

It has been noted in some exchange reactions, performed under neutral conditions, that the amino group and not the alkoxy group is replaced. 1,2-Diamines ° and l,3-diamines ° react with iminium salts, e.g. (139) by substitution of both the alkoxy and the amino group. - In lactim ester salts (140 equation 84) the alkoxy groups can be replaced in the same fashion. - ... 

The reductive couphng of imines can follow different pathways, depending on the nature of the one-electron reducing agent (cathode, metal, low-valent metal salt), the presence of a protic or electrophihc reagent, and the experimental conditions (Scheme 2). Starting from the imine 7, the one-electron reduction is facihtated by the preliminary formation of the iminiiim ion 8 by protonation or reaction with an electrophile, e.g., trimethylsilyl (TMS) chloride. Alternatively, the radical anion 9 is first formed by direct reduction of the imine 7, followed by protonation or reaction with the electrophile, so giving the same intermediate a-amino radical 10. The 1,2-diamine 11 can be formed from the radical 10 by dimerization (and subsequent removal of the electrophile) or addition to the iminium ion 8, followed by one-electron reduction of the so formed aminyl radical. In certain cases/conditions the radical 9 can be further reduced to the carbanion 12, which then attacks the... 

The mechanism of the Petasis boronic acid-Mannich reaction is not fully understood. In the first step of the reaction, upon mixing the carbonyl and the amine components, three possible products can form iminium salt A, diamine B, and a-hydroxy amine C. It was shown that preformed iminium salts do not react with boronic acids. This observation suggests that the reaction does not go through intermediate A. Both intermediate B and C can promote the formation of the product. Most likely, the reaction proceeds through intermediate C, where the hydroxyl group attacks the electrophilic boron leading to an ate -complex. Subsequent vinyl transfer provides the allylic amine along with the boronic acid sideproduct. 

Two in situ methods for the generation of N,A/-dimethyl(methylene)iminium salts, which are limited to reactions with enol silanes, are also available and avoid the need to handle these moisture-sensitive reagents. In the first method, iodide (30) is prepared in situ by treating methyl(methylene)diamine (34) with chloroiodomeAane (equation DMSO must be used as... 

Some comparisons between the yields of the Mannich reaction of enol silanes using in situ methods for preparation of the iminium salt and non in situ methods are shown in Table 9. Higher yields (20-30%) of P-amino ketones using in situ methods are seen in entries 2 and 4 but not in entry 1. Although a clear advantage of the in situ methods is not evident in these limited examples, in situ methods may be preferred from the standpoint of convenience. With aldehyde enol silanes (entry 3), the in situ method of Miyano et al is less practical due to elimination of the amino group, presumably caused by the strongly basic N,/V,/V, N -tetramethyl(methylene)diamine present in solution. 

Two in situ methods for the generation of A///-dimethyl(methylene)iminium salts, which are limited to reactions with enol silanes, are also available and avoid the need to handle these moisture-sensitive reagents. In the first method, iodide (30) is prepared in situ by treating methyl(methylene)diamine (34) with chloroiodomethane (equation 5) 36,37 DMSO must be used as solvent to achieve maximum yields. Cleavage of n-butyl dimethylaminomethyl ether (35) with TMS-I or TMS-OTf in MeCN comprises the second method (Scheme 5).38 A silyloxonium ion (36) was originally proposed as the reactive aminomethylating species, but a recent 13C NMR study of the reactions of ami-nol ethers with halosilanes in CD3CN-SO2 did detect the presence of iminium salts.39 Use of these methods in reactions with enol silanes is discussed in Section 4.1.2.2.2.iii. 

The reactions of iminium dithioate 120 are summarized in Scheme 27 [64]. The reaction of 120 with aniline takes place initially at the iminium carbon, prompting an iminium exchange reaction followed by deprotonation to produce a-imino dithioate 121. The same reaction also takes place for p-phenylene-diamine. The reaction with o-phenylenediamine occurs first at the iminium carbon and second at the dithioate carbon to give the quinoxaline 122. When morpholine is employed, the resulting iminium salt reacts further with another molecule of morpholine (when 2 equivs of morpholine is used) or methanol (solvent) to give a,a-dimorpholino dithioate 123 or a-methoxy-a-morpholino dithioate 124, respectively. 

In situ prepared iminium salts 201 in a concentrated ethereal solution of lithium perchlorate are very effective electrophiles in aza-MBH reactions and react with methyl acrylate in the presence of a catalytic amount of a tertiary amine at ambient temperature to afford aza-MBH adducts 202. The product undergoes conjugated addition with (trimethylsilyljdialkylamines to give the diamines 203 in good yields (Scheme 1.77). ... 

We identified an efficient DDQ-mediated CDC reaction between IV-phenyl THIQ and nitromethane that provides access to a number of rare chiral vicinal diamines [via 27d, Scheme 11.22). ° In the course of this work we observed NMR spectroscopic evidence for the long-supposed iminium ion and noted the precipitation of a solid in the reaction mixture which when isolated and then dissolved led to the reaction product. Subsequent focus on this solid using elemental analysis led to its suggested identity being 26c, where an iminium ion paired with the anion of the DDQ reaction product (the dihydroquinone) and this salt precipitated with another molecule of the protonated dihydroquinone (DDQHa). The solid was successfully... 

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