Lithium methyl deuterated derivative

Unlike the parent system, 5-methyl-5//-dibenz[c,e]azepine (1, R1 = Me R2 = H) on treatment with lithium diisopropyl amide fails to yield the tautomeric phenanthridine-imine (see Section 3.2.1.5.4.2.), but forms the 5-carbanion, which on quenching with deuterium oxide furnishes 5-methyl-[5-2H,]-5//-dibenz[e,e]azepine (l).83 5,7-Diphenyl-5//-dibenz[r,e]azepine (1. R1 = R2 = Ph) behaves similarly. In contrast, however, 5,7-dimethyl-5//-dibcnz[c,e]azepine (1, R1 = R2 = Me) yields theazaallyl anion 3, which on addition of deuterium oxide deuterates regiospecifically at the 7-methyl group to give derivative 4. 

Schemes 88 and 89, in which the lithium cation is coordinated to the sulfinyl oxygen and, in the former, with the sulfur lone pair also. Methyl iodide, which is a nonpolar substrate, prefers to react at the more nucleophilic side which is anti to the sulfur lone pair. It has been suggested, in other words, that the si and the re faces of the benzyllithium derived from S(s -(1) are hard and soft reaction centers respectively, whereas the same si face has both hard and soft reaction centers therefore the soft methyl iodide is expected to react at the re face in the first case and at the si face in the second one, which in fact explains the observed products. This type of rationalization also explains the stereochemistry of the protonation (deuteration) of these organometallics (for a controversal discussion see ref. 34).

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