Abstract:The C s -symmetrical cyclopropene 4a provided the palladacycle exo,exo-5 as the major product, accompanied by only small amounts of the endo,exo-5 isomer. The stereochemical assignments were accomplished by crystal structure analyses of the corresponding bpy, bis(acetone), and bis(acetonitrile) complexes. The enantiomerically pure, C 1 -symmetrical cyclopropene (S,S)-7, with two (S)-configured lactate units in the side-chain, delivered one dominant and three minor isomers. On the basis of one crystal structure… Show more
“…C 2 -symmetric compound 234 was obtained as a major product in a mixture with small amounts of other diastereomers (Scheme 78). 152 The tricylic complex of type 226 (Scheme 76), obtained from 1,2-unsubstituted cyclopropenes, is much more reactive and undergoes oligomerization with excess cyclopropene or other olefins present in the mixture to produce polycylic metallacycloheptane species 235 (Scheme 79). The latter can undergo reductive elimination to afford cyclohexane 236.…”
Section: Metallacyclization Reactionsmentioning
confidence: 99%
“…An alternative approach to optically active palladacycles involved metallacyclization of cyclopropene 233 bearing two ( S )-lactate auxiliaries. C 2 -symmetric compound 234 was obtained as a major product in a mixture with small amounts of other diastereomers (Scheme ) 77 78 …”
“…C 2 -symmetric compound 234 was obtained as a major product in a mixture with small amounts of other diastereomers (Scheme 78). 152 The tricylic complex of type 226 (Scheme 76), obtained from 1,2-unsubstituted cyclopropenes, is much more reactive and undergoes oligomerization with excess cyclopropene or other olefins present in the mixture to produce polycylic metallacycloheptane species 235 (Scheme 79). The latter can undergo reductive elimination to afford cyclohexane 236.…”
Section: Metallacyclization Reactionsmentioning
confidence: 99%
“…An alternative approach to optically active palladacycles involved metallacyclization of cyclopropene 233 bearing two ( S )-lactate auxiliaries. C 2 -symmetric compound 234 was obtained as a major product in a mixture with small amounts of other diastereomers (Scheme ) 77 78 …”
The different approaches for the synthesis of C,C-palladacycles are reviewed in this manuscript. These species hold a bidentate ligand that chelates the Pd atom through two C-donor moieties. Their relevance is closely related to the fact that they are intermediates in many palladium-catalyzed transformations. Furthermore, some of them have been used as efficient catalyst in cross coupling reactions. The review is structured according to the different strategies that have been employed to achieve the synthesis of the C,C-palladacycle derivatives, starting with those involving one elemental step (such as the oxidative addition of strained CÀ C bonds to Pd(0) or the transmetalation reactions between organometallic reagents and Pd(II) precursors), and continuing with more complex processes, where at least two elementary steps of Pd chemistry are involved (for example, carbometalation of alkenes followed by a CÀ H activation process). A final section highlights some aspects of synthetic methodologies based on Pd catalysis in which one or several C,C-palladacyclic intermediates are involved.Lenarda et al. synthesized the first reported four-membered C,C-palladacycles 1 a and 1 b in 1972, [5] via the oxidative addition of 1,1,2,2-tetracyanocyclopropane to [Pd(PPh 2 R) 4 ] (R = Ph; Me) (Scheme 1). The reaction occurred with the CÀ C bond cleavage of the highly strained ring and oxidative addition of the two resulting fragments to Pd(0).
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