Atomic alkyl amidinate

Oxidative attack on a carbon-hydrogen bond of an alkyl group a to a nitrogen atom is not restricted to saturated aliphatic amines. In fact X in an X-N-CH- structural subunit can be virtually any common atomic grouping that can be found in stable organic molecules. For example, w-carbon hydrogens of Aralkyl-substituted aromatic cyclic amines (119), aryl amines (120), amides (121), amidines (122), A-nitrosodialkylamines (123), etc. are all subject to oxidative attack, carbinolamine formation, and in most cases release of an aldehyde or ketone depending on the substitution pattern (1° or 2°)... 

Chemoselective E2 eliminations can be carried out with sterically hindered, sufficiently strong bases. Their bulkiness causes them to react with an H atom at the periphery of the molecule rather than at a C atom deep within the molecule. These bases are therefore called nonnucleo-philic bases. The weaker nonnucleophilic bases include the bicyclic amidines DBN (diazabi-cyclononene) and DBU (diazabicycloundecene). These can be used to carry out chemoselective E2 eliminations even starting from primary and secondary alkyl halides and sulfonates (Figure 4.17). 

The catalytic activation of allylic carbonates for the alkylation of soft car-bonucleophiles was first carried out with ruthenium hydride catalysts such as RuH2(PPh3)4 [108] and Ru(COD)(COT) [109]. The efficiency of the cyclopen-tadienyl ruthenium complexes CpRu(COD)Cl [110] and Cp Ru(amidinate) [111] was recently shown. An important catalyst, [Ru(MeCN)3Cp ]PF6, was revealed to favor the nucleophilic substitution of optically active allycarbonates at the most substituted allyl carbon atom and the reaction took place with retention of configuration [112] (Eq. 85). The introduction of an optically pure chelating cyclopentadienylphosphine ligand with planar chirality leads to the creation of the new C-C bond with very high enantioselectivity from symmetrical carbonates and sodiomalonates [113]. 

Basicity measurements of a great number of amidines have been conducted, both in solution and more recently in the gas phase. It was established that the basicity of amidines depends on the extent and type of substimtion at three sites at the amino and imino nitrogen atoms and at the functional carbon atom. Since the protonation occurs at the imino nitrogen atom, substitution at this site has the largest influence on the pK value of amidines, followed by the substitution at the functional carbon [45]. The pK values of alkyl-Al-substituted amidines measured in ethanol are presented in Table 2.3. Since these substituents show identical electronic effects, pK s are quite uniform along the series, and the values indicate a modest superbasicity at the lower part of the superbasicity scale. 

More than a third part of all the described principal syntheses of pyrimidines bearing fluorinated alkyl at C-4 atom commences from fluorinated p-dicarbonyl compounds 699. The chemistry of these bis-electrophiles was reviewed recently [411, 412] therefore, their preparation is not discussed herein. This synthesis of pyrimidines is fairly general (Table 34) it allows for introducing aliphatic, alicyclic and aromatic p-diketones (Entries 1-10), p-ketoesters (Entries 11-16), and cyclic P-ketoamides (Entry 17). Presence of some functional groups, such as additional ester moiety (Entry 15), is more or less tolerated, whereas increasing steric hindrance results in lowered yields of the products (Entry 10). A scope of conunon NCN binucleophiles include amidines (Entries 1, 11, 12, 17), (thio)urea and its derivatives (Entries 2-4), guanidines (Entries 5,16) and biguanides (Entry 6). Electron-rich amino heterocycles e.g. aminoazoles and even 2,6-diaminopyridine) are excellent NCN binucleophiles for the principal synthesis of fused pyrimidine derivatives (Entries 7-10, 13-15). 

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