Anionotropic

Reaction products of concomitant anionotropic 1,3-shifts to nitrogen and 1,5-shifts to carbon of sulfonyl groups in azo coupling products ofa-methoxy /J-oxo sulfones have been found under thermal conditions55,56 (equation 14). 

In the anionotropic system of sulphur dioxide (condensed below -10° C s x 16) we are concerned with an oxidotropic solvent with self-dissociation here the 02 ion does not exist in the free state, but occurs as the solvated ion SO3. A comparable situation is found in many systems of halotropy with self-dissociation, e.g., according to the overall reactions 4.30-4.33... 

Treatment of 89 with methanol gives rise to two products 112 and 113 (Scheme 46). The minor compound 113 is formed by protolytic cleavage of 1-boraadamantane, while the major product 112 is obtained as a result of coordination of alcohol to 89 and subsequent 1,2-anionotropic rearrangement <2001JOM(620)51>. 

Organoboration of diacetylenic derivatives proceeds stepwise and in a number of cases is also accompanied by 1,2-anionotropic rearrangement giving rise to polycyclic compounds (see Section 12.13.4.2) <2001CEJ775, 2002CEJ1537>. 

Secondary amines have been prepared from organoboron compounds R1315, R12 BC1 or R1BCI2 (R1 = Et, Bu, /-Bu,, v-Bu, 3-hexyl, cyclopentyl etc.) by treatment with azides R2N3 (R2 = Bu, /-Bu, i-Bu, cyclohexyl, Ph etc.) and aqueous work-up. It is suggested that the reactions proceed by way of anionotropic rearrangements (equation 61)176. 

An example of the anionotropic rearrangement is the reaction of propargyl halides with cuprous salts (Eq. 33). The mechanism and the role of the cuprous salt have not been-completely elucidated. 

Schlosser670 proposed an equivalent mechanism at the phosphorane 64 stage, formed from the corresponding ylide and not from the phosphonium salt the driving force for the migration comes from the carbenoid nature of the carbon in the a-position to the phosphorus. This is consistent with the anionotropic nature of the migration. The mechanism is corroborated by a similar migration from the ylide 65670 (reaction 198). 

The final product of the deprotonation depends strongly on the deprotonation reagent and/or the reaction conditions. Thus, in THF and using MeLi (or NaH) as base, an anionotropic l,3-Si,0-trimethylsilyl migration occurs in the alkoxymethylsilane 191 with formation of the silyl anion 192 instead of elimination of silanolate. Therefore, after hydrolytic work-up only trimethylsiloxy(bis(trimethylsilyl)silyl)alkanes 193 were obtained (equation 48).108,117... 

Lucchini, Pasquato, and co-workers have obtained stereoisomeric 2,3-disubstituted 1-methylthiiranium ions, reported characterization (1H and 13C NMR, X-ray crystallography), and studied their anionotropic rearrangements. The synthesis was performed by reacting methylbis(methylthio)sulfonium salts with alkenes184,185 (Scheme 4.7). 

A review on anionotropic 1,2-rearrangements of borate complexes evidences the most important factors that are responsible for which group migrates, by showing a broad spectrum of reactions involving borate complexes.17... 

In the reaction with spiroheptadiene, the unexpected compound 28 was isolated (equation 29)75. Its formation was a result of an anionotropic allylic rearrangement. 

The reaction of trialkylboranes with iV-chloroalkylamines can be used to synthesize a wide variety of functionally substituted dialkylamines in good yields [66,67], and it complements the synthesis of secondary amines via the reaction of trialkylboranes with organic azides. The reaction is analogous to the reaction of chloramine with organoboranes, and presumably occurs via an anionotropic migration of an alkyl group from boron to nitrogen (Scheme 24). 

Structures of thietanium tetrafluoroborate and hexachloroantimonate salts of 107, formed by anionotropic rearrangement of corresponding thiiranium salts, were obtained by X-ray crystallography and by calculation at the RHF/6-31G //RHF/6-31G level <2001HCA860>. 

Anionotropic rearrangements and displacement reactions yield allenes Allenes are also formed in basic media (Scheme 3.32). The reaction is particularly easy if the migrating hydrogen is adjacent to a second multiply bonded carbon. 

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