Rearrangement anions

With appropriately substituted oxetanes, aluminum-based initiators (321) impose a degree of microstmctural control on the substituted polyoxetane stmcture that is not obtainable with a pure cationic system. A polymer having largely the stmcture of poly(3-hydroxyoxetane) has been obtained from an anionic rearrangement polymerisation of glycidol or its trimethylsilyl ether, both oxirane monomers (322). Polymerisation-induced epitaxy can produce ultrathin films of highly oriented POX molecules on, for instance, graphite (323). Theoretical studies on the cationic polymerisation mechanism of oxetanes have been made (324—326). 

Anionic Rearrangement of Organosilicon and Germanium Compounds, 16, 1 Applications of 9mSn Mossbauer Spectroscopy to the Study of Organotin Compounds,... 

The ort/io-directing properties of the (aryloxy)tetrazole functionality has been demonstrated for the first time and rapid anionic rearrangement of the resulting lithiated derivative to form 5-(hydroxyaryl)-l-phenyl-l//-tetrazoles has been reported. ... 

A simple and flexible synthesis of benzoxathiin-2-one from phenols has been reported. The key step in this synthesis is a hitherto unknown anionic rearrangement under direct metallation conditions <2004T5215, 2003SL1474>. 

Scheme 61, yielded thiazole 200 as the major product, along with minor amounts of carbinol 201 [152]. On the other hand, treatment of the imine formed from 199 and p-methoxyphenylamine with catalytic tetrabutylammonium cyanide, produced suc-cinimide derivative 202. In both cases, the process is initiated by nucleophilic attack to the carbaldehyde C=0 (or azomethine s C=N) group, which is followed up by an anionic rearrangement. A variation of the above process using as catalysts /V-heterocyclic carbenes (NHC) derived from base treatment of azolium, imidazo-lium, or triazolium salts, has also been developed to access gem-disubstituted succinimides [153, 154]. Unfortunately, an attempt of kinetic resolution of racemic 4-formyl (3-lactams by using chiral NHC resulted in moderate selectivities only [154]. 

Later, he found equilibrium between the six- and the four-membered-ring anion, which depends very strongly on the temperature at which the reaction is conducted.41 Higher temperatures lead to a better Si->N contact across the ring and therefore isomerization is possible. Substitution is preferred at low temperatures. We have studied the anionic rearrangement in reactions with fluorosilanes and boranes and found three more factors that influence the equilibrium between the six- and four-membered rings illustrated in Scheme 18.42 43... 

Acrylic acid derivatives with a heteroatom (N, O, S, Hal) at C-3 can be cleanly deprotonated at this position with BuLi or LDA at low temperatures [329, 333-338] (Scheme 5.37). Some of these anions rearrange to the a-metalated acrylates on warming [329], but can also decompose (see Section5.4.7). Non-heteroatom-substi-tuted lithium /3-lithioacrylate [329] or /3-magnesioacrylic acid derivatives [339, 340] have been prepared by bromine-lithium or halogen-magnesium exchange. 

Eisch, J. J. Kovacs, C. A. Chobe, P. Carbon-skeletal [1,2] anionic rearrangements and the ir-orbital overlap constraint the question of nucleophilic attack vs electron transfer. J. Org. Chem. 1989, 54, 1275-1284. 

Neither 115 nor its radical anion rearranges to 116, so that both compounds are formed by the coupling of phenyl radicals with 114. The regioselectivity of the reaction has been proposed to be governed by the basicity of the system. 

The tandem carbolithiation-rearrangement of silyl derivatives constitutes also a useful synthetic methodology. The carbon—carbon bond formation is triggered by anionic rearrangement of a silyl group from carbon to oxygen and constitutes a new methodology for... 

Claisen rearrangement The Claisen rearrangement of highly substituted allyl vinyl ethers can proceed readily even when two vicinal quaternary centers are formed. Thus addition of an allylic alcohol (1) to an allenic sulfone (2) provides the allyl vinyl ether 3, whose anion rearranges at 50° to 4. Lithium dimsylate is the preferred base other counterions promote an undesirable side reaction.1... 

Finally, the allylcarbinyl/cyclopropylcarbinyl anion rearrangement (42a) (42b) should be mentioned as a striking example of a solvent-dependent valence isomerization [207]. 

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