Transpositional alkylations

Methylene homologation of vinylcoppers. Allylmetal species are formed, which undergo transpositional alkylation. 

Examples of alkylation, dealkylation, homologation, isomerization, and transposition are found in Sections 1,17,33, and so on, lying close to a diagonal of the index. These sections correspond to such topics as the preparation of alkynes from alkynes carboxylic acids from carboxylic acids and... 

This section contains alkylations of ketones and protected ketones, ketone transpositions and annulations, ring expansions and ring openings and dimerizations. Conjugate reductions and Michael alkylations of enone are listed in Section 74 (Alkyls from Alkenes). 

B2) 888 (Aj) methyl groups in transposition assignment acc. to local symmetry C21,. Compounds with higher alkyl substance are known, too (43)... 

This same concept applies to spiroannulations of six membered rings and is illustrated in a synthesis of acorenone B 155 as outlined in Scheme 547). The notion of alkylative carbonyl transposition permits the spiro enone 156 to become a logical intermediate. The standard analysis by a retro-aldol process translates the spiro ring system of acorenone B into a geminal alkylation problem as revealed by... 

Volume 75 concludes with six procedures for the preparation of valuable building blocks. The first, 6,7-DIHYDROCYCLOPENTA-l,3-DIOXIN-5(4H)-ONE, serves as an effective /3-keto vinyl cation equivalent when subjected to reductive and alkylative 1,3-carbonyl transpositions. 3-CYCLOPENTENE-l-CARBOXYLIC ACID, the second procedure in this series, is prepared via the reaction of dimethyl malonate and cis-l,4-dichloro-2-butene, followed by hydrolysis and decarboxylation. The use of tetrahaloarenes as diaryne equivalents for the potential construction of molecular belts, collars, and strips is demonstrated with the preparation of anti- and syn-l,4,5,8-TETRAHYDROANTHRACENE 1,4 5,8-DIEPOXIDES. Also of potential interest to the organic materials community is 8,8-DICYANOHEPTAFULVENE, prepared by the condensation of cycloheptatrienylium tetrafluoroborate with bromomalononitrile. The preparation of 2-PHENYL-l-PYRROLINE, an important heterocycle for the synthesis of a variety of alkaloids and pyrroloisoquinoline antidepressants, illustrates the utility of the inexpensive N-vinylpyrrolidin-2-one as an effective 3-aminopropyl carbanion equivalent. The final preparation in Volume 75, cis-4a(S), 8a(R)-PERHYDRO-6(2H)-ISOQUINOLINONES, il lustrates the conversion of quinine via oxidative degradation to meroquinene esters that are subsequently cyclized to N-acylated cis-perhydroisoquinolones and as such represent attractive building blocks now readily available in the pool of chiral substrates. 

The synthetic usefulness of dioxin vinylogous esters as p-keto vinyl cation equivalents was demonstrated by a variety of reductive and alkylative 1,3-carbonyl transpositions.5 7 Regioselective alkylation and hydroxylation at the a -position (and, in some cases, at the y-position)8 9 further extend the usefulness of 1,3-dioxin vinylogous ester templates in organic synthesis. 

The molecular ion appears to retain its cyclic structure, but several ions with two or three phosphorus atoms can be detected.192 The fragmentation patterns of a number of dialkylphosphines (157) show initial loss of an alkyl group as a neutral particle formed by the transposition of hydrogen.193 Some six-membered cyclic phosphites (158 X = OEt, OPh, or Cl) have been studied.194 The mass spectra of a wide variety of phosphine sulphides (159 Z = Ph, Me, CH2Ph, COPh, NH2, N=CHPh, or... 

Ketone rac-13 was transformed into the corresponding silylenolether and by Pd(II)-mediated Saegusa oxidation [14] into a, -unsaturated ketone rac-14. By alkylative enone transposition comprising methyl lithium addition and pyridinium chlorochromate (PCC) oxidation [15], rac-14 was finally converted into the racemic photo cycloaddition precursor rac-6. In conclusion, the bicyclic irradiation precursor rac-6 was synthesized in a straightforward manner from simple 1,5-cyclooctadiene (11) in nine steps and with an overall yield of 21%. 

The introduction of the double bond of rac-14 was performed by conversion of rac-13 into its a-phenylselenide, subsequent peroxide oxidation, and elimination. Following the synthesis reported by Mehta and Srinivas, an alkylative enone transposition was used as the last step towards irradiation... 

Scheme 9 Intramolecular sulfone alkylation and oxidative transposition...

The arylation reaction can be extended to bis- and tris-(dialkylamino)phosphines73, but in the case of iV-ethylanilinophosphine the reaction takes place with a rearrangement of the phosphasemidine type483. A structural transposition also occurs in the alkylation of some N-silylaminophosphines484-487 (reaction 141). Finally, it is noteworthy that, as far as the tris(dimethylamino)phosphine is concerned, many polyhalomethyltris-(dimethylamino)phosphonium salts have been prepared by the action of the appropriate polyhalomethanes (reaction 142). 

Alkylation of allylnitroalkanes.9 Cyclic allylic nitro compounds react with stabilized carbanions or amines in the presence of Pd(0) at the allylic position without allylic transposition. The reactive intermediate is presumably an allylpalladium(Il) species. 

The delocalization of enolate allows a transposition into an enol mercapto phosphate which can be quite easily alkylated. Then enol phosphate thioethers 12 can be obtained. 

In fact, the aldehydic product could be alkylated with a vinyl anion, and the subsequent double [2,3] sigmatropic rearrangement at room temperature furnished 23 as a 3 1 mixture of epimers. Camphorsulfonic acid induced the transposition of the substrate into a bis(tetrahydrofuran) derivative. Pummerer... 

A second route involves preforming first the allylic halide addition to form the iminium salt arising from the alkylation on the highly nucleophic sulfur atom. Subsequent treatment with triethylamine provided the S-allyl thioimidoester which was usually not observed but underwent a deprotonation and a fast [3,3] sigmatropic transposition to give the a-allyl thioamide. With pyroglutamate derivatives no diastereoselectivity was found. An analogous sequence [197] was used with a thioacyl proline derivative, with some stereoselectivity. 

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