Palladium catalysis rearrangements

The synthesis of thiepins 14 was unsuccessful in the case of R1 = i-Pr,79 but if the substituents in the ortho positions to sulfur arc /erf-butyl, then thiepin 14 (R1 = t-Bu R2 = Me) can be isolated in 99% yield.80 Rearrangement of diazo compound 13 (R1 = t-Bu R2 = H), which does not contain the methyl group in position 4, catalyzed by dimeric ( y3-allyl)chloropalladium gives, however, the corresponding e.w-methylene compound. The thiepin 14 (R1 = t-Bu, R2 = H) can be obtained in low yield (13 %) by treatment of the diazo compound with anhydrous hydrogen chloride in diethyl ether at — 20 C.13 In contrast, the ethyl thiepin-3,5-or -4,5-dicarboxylates can be prepared by the palladium catalysis method in satisfying yields.81... 

The rearrangement of polyfluoroalkyl-substitutcd alkynes 7 to 1 if,377-dienes 8 can be achieved with palladium catalysis.59... 

Several mechanisms have been proposed for palladium catalysis of Cope rearrangements. Overman, who has examined metal ion catalysis of a number of 3,3-sigmatropic rearrangements, considers this an... 

The a-allylpalladium intermediate 135a, which must be formed on coupling of l,3-dicyclopropyl-l,2-propadiene (134), with, for example, iodobenzene under palladium catalysis rapidly undergoes rearrangement to the homoaUylpalladium species 135b and subsequent P-hydride elimination to yield the 1,3,5-hexatriene 136 [152g,h]. This in turn undergoes [4 + 2] cycloaddition with an added dienophile to furnish the 3-(2-cyclopropyl-l-phenyl)cyclohexene derivatives 138 as a mixture of trans,trans- and ds,trows-diastereomers (Scheme 8.31). 

Moreover, the Newman-Kwart rearrangement has also been shown to work under microwave radiation [39a], in scale-up procedures [40], as well as being made more practicable with the incorporation of a palladium catalysis step enabling a reduction in reaction temperatures to be obtained [41]. 

Cyclic secondary amines are also produced by the ring expansion of O-sulphonyloximes via a Beckmann rearrangement/ the cyclization of a,aliphatic diamines by a ruthenium catalyst/ the palladium-promoted ring closure of amino-alkenes/ and the sulphonamidomercuration of 1,4- and 1,5-dienes. The latter two reactions form part of a wealth of new literature on the amination of olefins and acetylenes via aminomercuration " and via palladium catalysis. ... 

This outcome can be explained by a shift from the chair transition state (Broensted acid) to a boat-hke transition state in the palladium catalysis. This very much encourages investigation of rearrangements that are confined to a boat transition state, such as compounds of type 384 [140]. 

The usual cyclopropanation reagent, diazomethane and diazoacetates, react smoothly with alkenes in the presence of palladium-catalyst to form cyclopropanes. However, it should be noted that rhodium complexes serve in most cases as superior catalyst. Cyclopropanes can be formed from alkenes (dienes) and nucleophiles using oxidative palladium catalysis (Scheme 5-175). In this case, copper(II) salts regenerate the palladium(II) complexes. The vinyl cyclopropanes produced undergo subsequent vinylcyclopropane-cyclopentane rearrangement to form bicycles. ... 

The observed regiochemical outcome of this reaction was contrary to those of other related rearrangements of 0-allyl or S -allyl phosphonothionates and dithiocarbonates under palladium catalysis where linear sulfone products... 

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