Butadiene, catalyzed reactions cyclization

Pd-cataly2ed reactions of butadiene are different from those catalyzed by other transition metal complexes. Unlike Ni(0) catalysts, neither the well known cyclodimerization nor cyclotrimerization to form COD or CDT[1,2] takes place with Pd(0) catalysts. Pd(0) complexes catalyze two important reactions of conjugated dienes[3,4]. The first type is linear dimerization. The most characteristic and useful reaction of butadiene catalyzed by Pd(0) is dimerization with incorporation of nucleophiles. The bis-rr-allylpalladium complex 3 is believed to be an intermediate of 1,3,7-octatriene (7j and telomers 5 and 6[5,6]. The complex 3 is the resonance form of 2,5-divinylpalladacyclopentane (1) and pallada-3,7-cyclononadiene (2) formed by the oxidative cyclization of butadiene. The second reaction characteristic of Pd is the co-cyclization of butadiene with C = 0 bonds of aldehydes[7-9] and CO jlO] and C = N bonds of Schiff bases[ll] and isocyanate[12] to form the six-membered heterocyclic compounds 9 with two vinyl groups. The cyclization is explained by the insertion of these unsaturated bonds into the complex 1 to generate 8 and its reductive elimination to give 9. 

Among transition metal complexes used as catalysts for reactions of the above-mentioned types b and c, the most versatile are nickel complexes. The characteristic reactions of butadiene catalyzed by nickel complexes are cyclizations. Formations of 1,5-cyclooctadiene (COD) (1) and 1,5,9-cyclododecatriene (CDT) (2) are typical reactions (2-9). In addition, other cyclic compounds (3-6) shown below are formed by nickel catalysts. Considerable selectivity to form one of these cyclic oligomers as a main product by modification of the catalytic species with different phosphine or phosphite as ligands has been observed (3, 4). 

Nckel catalyzed steroeselective synthesis ol cis and trans methyl vinykryclopentanes Irom telemerization of butadiene Cyclization (ene reaction) of unsaturated ellyl Qrignard reagents... 

Unlike nickel Catalysts, palladium complexes do not catalyze the homo-cyclization reaction to give CDT or COD. The difference seems to be due to a different degree of hydride shift and atomic volume. With palladium catalysts, the hydride shift is easier, and hence linear oligomers are formed. The characteristic reaction catalyzed by palladium is the cocyclization of two moles of butadiene with one-hetero atom double bonds such as C=N and C=0 bonds to give six-membered rings with two vinyl groups (19) ... 

This preparation is based on a procedure published by the submitters. 9-Phenylphenanthrene has been prepared previously by the reaction of phenyllithium with 9-chlorophelianthrene, by the high-temperature dehydrogenation with palladimn on charcoal of the Diels-Alder dimer of 1-phenyl-1,3-butadiene, and by the acid-catalyzed cyclization of the alcohol formed from the reaction of 2-biphenylylmagnesium iodide and 2-phenoxy-acetophenone. ... 

A variant of this process, studied by DuPont and DSM [32c], includes the hydrocarboxylation (hydroxycarbonylation) of butadiene with carbon monoxide and water this technology offers potential savings in raw material costs. The reaction primarily yields 3-pentenoic acid using a palladium/crotyl chloride catalyst system, with a selectivity of 92%. Further conversion of pentenoic acids by reaction with carbon monoxide and methanol and a palladium/ferrocene/phosphorous ligand catalyst has demonstrated a selectivity to dimethyl adipate of 85% the latter is finally hydrolyzed to AA. The main problem in this reaction is the propensity of pentenoic acid to undergo acid-catalyzed cyclization to y-valerolactone one way to circumvent the problem is to carry out the hydrocarboxylation of pentenoic acid using the y-valerolactone as the solvent. 

Nickel and Grignard catalyzed stereoselective synthesis of cis and trans 2-alkyl-vinylcyclopentanes from telemerization of butadiene. Cyclization (ene reaction) of unsaturated allyl Grignard reagents, see also Feldman (see 1st edition). 

Only the E,3E stereoisomer of the 2-azadiene was found to be reactive under the reaction conditions. Consequently, each of the piperidine products was found to possess the cis 2-phenyl, 5-methyl relative stereochemistry. Moreover, the cycloaddition products derived from reactions of enol ethers possessed the all-cis 2-phenyl-4-alkoxy-5-methyl stereochemistry necessarily derived from exclusive endo cycloaddition. Dienophile geometry is maintained during the course of the [4 + 2] cycloaddition, and no products derived from a potential stepwise, addition-cyclization reaction were detected. Representative neutral and electron-deficient dienophiles failed to undergo cycloaddition. A related boron trifluoride etherate-catalyzed [4 + 2] cycloaddition of simple 2-aza-l,3-butadienes with carbonyl compounds provides 5,6-dihydro-2//-l,3-ox-azines and appears to proceed preferentially through an endo [4 + 2] transition state although evidence supporting a stepwise, addition-cycli-zation was occasionally detected.630... 

Other aldehydic compounds, such as glyoxal and chloral, also react in a similar way with polyisoprenes and unsaturated rubbers (e.g., poly(cfs-l,4-isoprenes), poly( fs-l,4-butadiene), and copolymers of isobutylene and iso-prene). The use of strong acids, or Lewis acids, causes complications, as the acids themselves, under suitable conditions, catalyze cyclization and cis-trans isomerization, and these reactions may occur simultaneously with the addition reactions. 

It is well known that Ni(0) catalyzes the cyclodimerization and cyclotrimer-ization of butadiene to form COD or CDT. On the other hand no cyclization of butadiene occurs with Pd(0) catalyst. Pd(0)-catalyzed dimerization of butadiene to form 1,3,7-octatriene (1) is the main reaction. 

Metal-mediated cyclizations that rely on the initial complexation of an alkene or alkyne around a low oxidation state metal center are often sensitive to the presence of additional substituents (particularly electron-donating substituents), and relatively more stringent reaction conditions are often required for successful cychzation. This effect was noted in the Ni-catalyzed formal [4 -I- 4] cycloaddition reactions developed by Wender and Tebbe and is apparent when one compares the reported facility of Pd-catalyzed linear dimerization of 1,3-butadiene versus that of substituted 1,3-dienes. Similarly, the initial attempts at Pd-catalyzed cyclization of bisdiene 70a (Scheme 22) were rather disappointing. Using 0.05 equiv of [Pd(OAc)2/3 PhjP] (THF, 65 °C, 12 h), only a small... 

Another photocatalytic reaction of some interest is the cyclic dimerization of alkenes, which has been reported for a number of different metal carbonyls including Fe(CO)s, Cr(CO)6, Ni(CO)4 and several substituted analogs [83-85]. Although such dimerizations are catalyzed thermally by some of the same species, the stereochemistries of the products differ depending both upon which complex is utilized and whether the reaction is carried out thermally or photochemically. The dimerization of butadiene to 4-vinylcyclohexene photocatalyzed by the iron dicarbonyl Fe(CO>2(NO)2 has been studied by examining the intermediates formed when the photolysis was carried out in liq. Xe [85]. The key species was found to be the disubstituted species Fe(NO)2(Ti -butadiene)2 which was proposed to undergo isomerization to Fe(NO)2( n -butadiene)(ri2-butadiene) which can undergo an internal Diels-Alder cyclization to the vinyl cyclohexene. 

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