Conjugated diene complexes cyclic

Binaphthol-derived titanium complexes [64], prepared from chiral ligands 65 (Figure 3.13), also performed very well in the cycloadditions of conjugated aldehydes with cyclic and acyclic dienes. Judging from the absolute configurations of endo and exo adducts, this catalyst should cover the re-face of carbonyl on its u tz-coordination to s-trans a,/l-unsaturated aldehydes, and hence dienes should approach selectively from the si-face. 

Of mechanistic interest is the question of whether these cyclic ketones come directly from conjugated diene intermediates or from PdCl2 complexes of carboxyoctadecenoates. Yields of cyclic ketones 4 are actually of the same order of magnitude from linoleate as from its conjugated diene isomers (Runs 7 and 8, Table I). Studies were also made to determine if yields of cyclic ketones can be influenced by the amount of H20 used. However, in experiments using no added H20 and one-tenth the stoichiometric amount of H20, only 10 and 8% ketones and conversions (diene disappearance) of only 58 and 78% were obtained, respectively. 

In the presence of triethylamine, decomposition of the ir-allylic complexes to conjugated dienes may occur, particularly when electron-withdrawing substituents are present on a methyl group in the 1- or 3-position of the iT-allyl system.31 Cyclic alkenes and vinylpalladium chlorides also yield iT-allylic complexes in the absence of an amine. If a tertiary amine is present, however, l,4-dienes are obtained (equation 1l).32... 

Reaction of the carbene complex 148 with alkyne affords vinylcarbene 150 via metallacyclobutene 149. In the intramolecular reaction of enyne 152, catalysed by carbene complex 151, the triple bond is converted to vinylcarbene 153 which then reacts with the double bond to give the conjugated diene 154. Generation of 154 is expected by the formation and cleavage of cyclobutene 155 as a hypothetical intermediate. Based on this reaction, Ru-catalysed intramolecular metathesis of enyne 156 gave the N-containing cyclic diene 157, from which (—)-stemoamide (158) was synthesiszed. The reaction can be understood by assuming the formation of the hypothetical cyclobutene 159 from 156 [52],... 

The achiral aziridination with the racemic nitrido complex 15 was successfully applied to a wide range of 1,3-dienes (Table 6.6). Cyclic conjugated dienes were smoothly aziridinated under mild conditions with no [4+1] adducts. Among these, cyclohexadiene and cycloheptadiene reacted with the complex in good yields. When the unsymmetrical dienes were employed in the reaction, the aziridi-nations of isoprene and trans-1,3-hexadiene proceeded, giving two regioisomers in 70 30 and 94 6, respectively. The major isomers in both reactions were formed by the aziridination of the less substituted olefins of the 1,3-dienes. 

The intermediate case where a complex is formed but opening occurs spontaneously to only a limited extent is illustrated by the reaction of butadiene or other conjugated dienes with sulfur dioxide (16). When the two components react, a cyclic adduct and a linear alternating copolymer are produced simultaneously. 

The complex [OsHBr(CO)(PPh3)3] is effective for the selective hydrogenation of conjugated and non-conjugated dienes to monoenes, and this complex also catalyzes the hydrogenation of linear and cyclic alkenes. (-)-Carvone (9) is selectively reduced to 2-methyl-5-(l-methylethyl)cyclohex-2-en-l-one (10) or 2-methyl-5-(l-methylethyl)cyclohexanone (11), depending on the reaction conditions. ... 

The asymmetric hydrosilylation of a-methylstyrene with methyldi-chlorosilane has been catalyzed by (/ )-benzylmethylphenylphosphine complexes of platinum(II) 302) or nickel(II) 304) to give a 5 or 17.6% excess of one enantiomer in the addition product, 2-phenylpropyl-methyldichlorosilane. The corresponding palladium(II) complexes were, however, only slightly useful for asymmetric synthesis in hydrosilylation of olefins. Nevertheless, palladium(II) complexes of methyldiphenyl-phosphine or epimeric neomethyldiphenylphosphine, where the dissymmetry is remote from the phosphorus, are especially useful for the induction of asymmetry in the hydrosilylation of styrene and some cyclic conjugated dienes 199). A similar procedure has been used for... 

Dicarboration of conjugated dienes can occur in either a 1,2- or a 1,4-addition mode. Several examples of stepwise stereoselective c -l,4-dicarborations of open-chain and cyclic dienes, via palladium-allyl complexes, which use stoichiometric amounts of palladium salts and soft, delocalized carbanions have been reported65 67. Catalytic dicarboration of 1,3-butadiene, stereoselectively leading to ( )-alkenes with up to 70% yield, is achieved using aryl iodides and delocalized carbanions of the malonate type in the presence of palladium(II) chloride and l,2-bis(diphenylphosphino)ethane68. A Tt-allyl-palladium intermediate is thought to determine the E geometry of the product. 

---