Hydroxylamines, addition with organometallics

Nucleophilic addition of organometalic reagents occurs when the nitrone form is in equilibrium with the hydroxylamine form, for instance, in the case of N -benzyl-/V-glycosyl hydroxylamines (Scheme 2.130) (213). 

Addition of organometallic reagents to nitro compounds is possible but is sparingly used. Reaction of aromatic nitro compounds with large excess of phenyl magnesium bromide produces hydroxylamines in moderate yield . Similar addition of Grignard compounds to nitromethane proceeds in low yield ° while addition of excess methyllithium to tertiary nitro compound 113 results in formation of hydroxylamine 114 (equation 83) . ... 

The addition of ( )-(3-trimcthylsilylallyl)boronate (10) to the racemic oxime 9 has been used in connection with a total synthesis of cannabisativine n. The results are congruent with the application of ( )-crotylboronatc as organometallic reagent9,, 0. The reaction is anti selective and generates the diastereomeric hydroxylamines 11 and 12, where 11 is converted to a tetrahydropyridine 13, a useful intermediate for the synthesis of cannabisativine11. 

O - P h e n y 1 - /V - e r y t h r o s y 1 nitrone (336), as a Ci,C i-bis-electrophile, when subjected to the double addition of Grignard reagents (in a domino style), leads to acyclic hydroxylamine (338) via the formation of open-chain nitrone (337 ). The reaction proceeds at 0°C with variable diastereoselectivity ranging from medium to good, depending on the organometalic reagent used (Scheme 2.140) (564). 

In consequence, addition to the ethylenic carbon atom (1) often occurs in these conjugate systems with reagents that do not usually add to ethylenic double bonds. Thus the cyanide ion of HCN, the sulfite ion of bisulfites, the nitrogen of hydroxylamine and of ammonia, and the alkyl group of organometallic compounds are all... 

Disubstituted nitroxides constitute a well-known class of rather stable free radicals. N,N-disubstituted anions of organometallic hydroxylamines have just one additional electron more than the corresponding nitroxide. Oxidation of the rearranged anions of silyl or germylhydroxyl amines, electrolytically or with oxygen, produces solutions of organometal nitroxides (30). Examples are shown in Eqs. (19)-(21). These nitroxides are stable in dilute solution for several days at room temperature. 

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