Anionic rearrangement

The reaction is probably initiated by fluoride attack on the carbonyl group, as shown in Figure Si6.12. A Brook rearrangement, anion quenching, and fluoride-induced collapse of the tetrahedral intermediate then complete a plausible pathway for this transformation. 

The anions 13 of the N.O-substituted hydroxylamines 12 are in equilibrium with the rearranged anions 14. Oxidation by oxygen or electrolytically yields the corresponding aminyloxides 16. Abstraction of hydrogen from 12 also yields aminyl-oxides 16 which must be formed by rearrangement of the intermediate radical 1530 ... 

For a more complex example of this type of rearrangement (anionic Claisen rearrangement of a tricyclic a-allyloxy ketone) see ref 108. 2-Allyloxy-3-methyl-2-cyclohexenones109 111 and nitrogen derivatives thereof112 rearrange in a different way. 

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. 

ARC process [67]. The initiating nucleophiles included either lithiated 2-methyl-1,3-dithiane or lithium di-n-butylcuprate, which on reaction with these linchpins (191-193), followed by trapping of the rearranged anion 172 by allyl bromide as electrophile, provide three-component adducts such as 194-196 in 58-68% overall yields (Scheme 4.38) [63, 67]. Of particular note is the stereochemical outcome of these reactions. High diastereoselectivity was observed with linchpins possessing a methyl substituent a to the silyl group, when a phenyl moiety serve as ASG (Scheme 4.38, Eq. (2)), while poor diastereoselectivity is observed when a phenylthio moiety is employed as the ASG irrespective of the presence of a-substituent (Scheme 4.38, Eq. (3)) [67, 68]. 

If there is an o-fluorine-substituted phenyl group in the amide fragment, attack by the rearranged anion 301 leads both to cycUzation with substitution of the nitro group in one of the aryl fragments and the formation of the pyrroloquinoxaline 302 and to substitution of the fluorine atom in other aryl group and the formation of pyrroloquinoxaline 303 (Scheme 3.92) (Rotas et al. 2004). 

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