Allylic rearrangement, promoted

Similar reactions under basic conditions are mechanistically ambiguous. They can either be regarded as norcaradiene to cycloheptatriene valence isomerizations or as cyclopropyl to allyl rearrangements promoted by exocyclic proton abstraction. ... 

The first hydration step was promoted by Bronsted acids containing weakly or noncoordinating anions. In the second step, an intramolecular hydrogen transfer in the secondary alcohol was catalyzed by ruthenium(III) salts with chelating bipyridyl-type ligands. The possible complexation of the latter with the diene did not inhibit its catalytic activity in the allylic rearrangements, under acid-catalyzed hydration conditions. 

Oxidation of 3-acetoxy-l-nonene (14) at 50 C gave a mixture of the methyl ketone (15) and 1-ace-toxy-3-nonanone (16) in 33% and 17% yields. The latter was formed by regioselective oxidation of 1-acetoxy-2-nonene, itself formed by the allylic rearrangement of (14) promoted by Pd ions (equation 11). 

Allylchlorostannanes react with acyl chlorides in the absence of any added catalyst, the chlorostannane having sufficient Lewis acid character to promote acylation with allylic rearrangement (equation 26). Similarly, no added catalyst appears necessary for acylations of alkynylstannanes, although the tri-alkylchlorostannane formed in the thermal acylation may exert a catalytic influence on the reaction. 

Although electron-transfer-promoted reactions of 89 are unknown, cation radical 95 has been generated by y-irradiation and its matrix-dependent reactivity was recently reported by Gerson and his co-workers. In a CF3CCI3 matrix at 77 K, 95 rearranges rapidly to the bisected tetramethyleneethane cation radical 96. However, deprotonation occurs at 120 K in a CFjClCFClj matrix to form 97 (Scheme 26). It is reasonable to assume that cation radical 96 is formed by the cyclopropyl-allyl rearrangement of 94 itself generated from 95. ... 

Palladium.—number of papers have appeared dealing with the many facets of allyl rearrangement in A -allyl complexes of palladium. The criteria for tackling these often complicated systems have already been outlined in this section in Volume 2 of these Reports and need no further mention here. For the sake of convenience the reports will be dealt with in two categories, intrmnolecular rearrangements and rearrangements promoted by substitution. 

Rearrangements Promoted by Substitution, syn-anti Proton site exchan in [Pd(A -allyl)(diphos)]X (X = PFg or BF4 A -allyl may be substituted) is accelerated by an added base such as pyridine. The results indicate an 5 n2 substitution process as in Scheme 4 and not an allyl rotation as previously proposed. In comparison, syn-syn and simultaneous anti-anti site exchange... 

Rearrangements. Allyl vinyl ethers undergo [3,3]-sigmatropic rearrangements promoted by EtsAl, which also effects subsequent ethylation of the resulting aldehydes (eq 13). Use of Triisobutylahiminum leads to primary alcohols by P-hydride reduction. ... 

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