Carbon dioxide, addition dienes

Ozonolysis of diketone carbonate 417 in methanol afforded an almost quantitative yield of the bicyclic diene triketone hydroxy-ester 418 (119). This remarkable transformation can also be readily explained. Ozonolysis of 417 produces the tetraketone intermediate 419 followed by methanol addition to produce the hemi-ketal 420 which undergoes a retro-Claisen reaction to 421. Then, loss of carbon dioxide from 421 yields 418. Again, 420 could also undergo a Grob type fragmentation to yield 418 directly. 

In the past, this field has been dominated by ruthenium, rhodium and iridium catalysts with extraordinary activities and furthermore superior enantioselectivities however, some investigations were carried out with iron catalysts. Early efforts were reported on the successful use of hydridocarbonyliron complexes HFcm(CO) as reducing reagent for a, P-unsaturated carbonyl compounds, dienes and C=N double bonds, albeit complexes were used in stoichiometric amounts [7]. The first catalytic approach was presented by Marko et al. on the reduction of acetone in the presence of Fe3(CO)12 or Fe(CO)5 [8]. In this reaction, the hydrogen is delivered by water under more drastic reaction conditions (100 bar, 100 °C). Addition of NEt3 as co-catalyst was necessary to obtain reasonable yields. The authors assumed a reaction of Fe(CO)5 with hydroxide ions to yield H Fe(CO)4 with liberation of carbon dioxide since basic conditions are present and exclude the formation of molecular hydrogen via the water gas shift reaction. H Fe(CO)4 is believed to be the active catalyst, which transfers the hydride to the acceptor. The catalyst presented displayed activity in the reduction of several ketones and aldehydes (Scheme 4.1) [9]. 

In addition to the polymerization of dienes the versatility of NdP-based catalysts is exceptional regarding the number of different non-diene monomers which can be polymerized with these catalysts. Acetylene is polymerized by the binary catalyst system NdP/AlEt3 [253,254]. Lactides are polymerized by the ternary system NdP/AlEt3/H20 [255,256]. NdP/TIBA systems are applied in the copolymerization of carbon dioxide and epichlorhy-drine [257] as well as for the block copolymerization of IP and epichloro-hydrin [258]. The ternary catalyst system NdP/MgBu2/TMEDA allows for the homopolymerization of polar monomers such as acrylonitrile [259] and methylmethacrylate [260]. The quaternary system NdP/MgBu2/AlEt3/HMPTA is used for the polymerization of styrene [261]. 

Addition of water to dienes is catalyzed by palladium complexes. The reaction has been used for synthesizing unsaturated alcohols and ethers from aliphatic conjugated C4 and Cg olefins 248). In particular, the hydration of butadiene with water in the presence of bis(2,4-pentane-dionato)palladium and triphenylphosphine gave 2,7-octadien-l-ol, l,7-octadien-3-ol, and 1,3,5,7-octatetraene 18). The reaction was accelerated by carbon dioxide. Compounds Pd(PPh3)4 and Pd(02C0)-(PPh3)2 were also effective. 

When 2 was treated with only one equivalent of acetone, no product derived from the reaction of 2 with two molecules of acetone was observed, indicating that in the presence of 2, the initially formed adduct 12 did not add competitively to the unreacted acetone. This feature allowed both acetone and, subsequently, added carbon dioxide to be delivered to the original diene at the desired positions. However, if excess acetone was used, 12 underwent further nucleophilic addition to the ketone, yielding the corresponding diol. Therefore, it was essential to not use more than 1 Eq of acetone for the synthesis of 16. 

Ditertiary phosphane complexes of nickel were found to be effective in the formation of pyrone 108 by cyclocotrimerization of alkynes with carbon dioxide. The formation of the nickelacyclopentadiene 105 from two moles of alkyne and a nickel complex is followed by CO2 insertion into a nickel-carbon bond to give the oxanickelacycloheptadienone 106, which then eliminates 108 with intramolecular C—O coupling. Another route involving [4 + 2] cycloadditions of 105 with CO2 in a Diels - Alder reaction to give 107 cannot be ruled out but is less probable because CO2 does not undergo [4 + 2] cycloaddition with dienes. Addition of another alkyne to 105 results in the formation of a benzene derivative (Scheme 38). ... 

Pyrone reacts readily as a diene in Diels-Alder additions, but the initial adduct often loses carbon dioxide, generating a second diene that then adds a second mole of the dienophile reaction with maleic anhydride, shown below, is typical - a monoadduct can be isolated, which under more vigorous conditions loses carbon dioxide and undergoes a second addition. When the dienophile is an alkyne, methyl propiolate for example, benzenoid products result from the expulsion of carbon dioxide. Primary adducts, which have not lost carbon dioxide, can be obtained from reactions conducted at lower temperatures under very high pressure or in the presence of lanthanide catalysts. A useful example is the reaction of 2-pyrone and substituted derivatives with alkynyl boronates leading to aryl boronates 2-pyrone itself reacts in 86% yield with trimethylsilylethynyl boronate. ... 

An intermolecular Diels-Alder reaction of 3,4-pyridyne has been used in a short synthesis of the important anticancer alkaloid eUipticine. In this case the diene is an a-pyrone the initial Diels-Alder adduct is not isolated since it spontaneously aromatizes by loss of carbon dioxide. Unfortunately, the Diels-Alder reaction is not regioselective and an equal amount of the product arising from the alternative direction of addition to 3,4-pyridyne is formed (Scheme 7.35). 

ABSTRACT The review covers particularly the synthesis of fine chemicals via the formation of C-C bonds between carbon dioxide and hydrocarbons. In the reactions of CO2 with alkenes, dienes and alkynes a great number of carboxylic acids, dicarboxylic acids, esters, lactones and pyrones are formed, whether in stoichiometric or catalytic reactions. In each chapter the reactions are considered in the order of the transition metals applied. In addition, some syntheses will be mentioned which are closely related to transition metal catalysis, for instance the electrocarboxylation ofolefinic hydrocarbons. 

Carbon dioxide reacts with 1-hexyne to give 4,6-dibutyl-2-pyrone in addition to tributylbenzenes " [equation (13.239)]. A stoichiometric reaction of dienes with CO2... 

Heterosubstituted endocyglic dienes have also been used. In addition to furans [50-53], alkoxydienes [54, 55], benzopyrroles [56], and dihydropyridines [57] have been employed. It should be noted that addition to furans is readily reversible [53]. This difficulty has been overcome by using a pyrone dienophile [54]. Loss of carbon dioxide from the cycloadduct makes the addition irreversible. 

The Nobel Laureates involved in cycloaddition chemistry include Sharpless (2001), Staudinger (1953), Diels and Alder (1950) and Wittig (1979) and today s emphasis on green chemistry has accelerated research in this field. For example, cycloaddition reactions of carbon dioxide could be of interest for sequestering of greenhouse gases. In addition, sulfur dioxide readily undergoes cycloaddition reactions with dienes. 

It has been reported that a retro-oxidative cyclization process proceeds in catalytic C-C bond cleavage reactions. For example, a six-membered cyclic allylic carbonate 38 underwent a palladium-catalyzed decarboxylative C-C bond cleaving reaction to afford dienyl aldehyde 40 (Scheme 7.12) [15]. It is proposed that oxidative addition of the allylic carbonate to palladium(O) followed by elimination of carbon dioxide generates the palladacycle 39. Subsequent retro-oxidative cyclization produces the diene and aldehyde functionalities. 

Another way to circumvent the stereoselectivity issues that may arise from olefination or addition/elimination sequences to l,4-dien-3-ones is to switch the polarity of components and olefinate a carbonyl compound with a symmetrical nucleophilic pentadienyl anion equivalent. A seminal contribution was reported by Paul and Tchelitcheff in 1951, who combined trivinylmethane (235) and carbon dioxide to form a [3]dendralene 237 (Scheme 1.40 (a)) [190]. In this instance, the anion of trivinyl methane 236 is indeed a pentadienyl anion, but bond formation occurs with allylic transposition through a vinyl unit. 

Upon alkaline fusion of lupulone the following acids and ketones have been obtained, in addition to carbon dioxide acetic acid and 5-(3-methyl-2-butenyl)-2,10-dimethylundeca-2,9-dien-6-one 5-methyl-4-hexenoic acid and 3-(3-methyl-2-butenyl)-6-methyl-5-hepten-2-one 2-(3-methyl-2-butenyl)-5-methyl-4-hexenoic acid and 6-methyl-5-hepten-2-one (see also 14.4.). The position of the double bonds in these compounds has been confirmed by ozonolysis, whereby only acetone was isolated, The same result has been obtained by direct ozonization of lupulone (9,10). Consequently, lupulone is the enolized 2-(3-methylbutanoyl)-4,6,6-tris-(3-methyl-2-butenyl)-cyclohexane-1,3,5-trione (23, Fig. 77). The structure has been proved by synthesis (see 11.4.). 

Addition, acetic acid to bicyclo[2.2.1]-hepta-2,5-diene to give nortri-cyclyl acetate, 46, 74 1,2,3-benzothiadiazole 1,1-dioxide to cyclopentadiene, 47, 8 benzyne to tetraphenylcyclopentadie-none, 46,107 Br, F to 1-heptene, 46,10 carbon tetrachloride to olefins, 46, 106... 

Takaki reports that ketone enolates add to dimethylstyryl sulfonium perchlorate (155) or methyl styryl sulfone (156) in a Robinson-type annulation sequence to afford the corresponding 3-hydroxythiadecalin (157) or 5-dioxide (158), respectively subsequent reductive desulfonation of (158) affords diene (159).131 However, additions to acceptor (155) suffer from competing cyclopropanation which is dependent on the electrophilicity of the carbonyl group and the ring size of the ketone (Scheme 61). As an aside, DeLucchi reports that l,l-bis(benzenesulfonyl)ethylene (160) adds to ketones at the more substituted a-carbon under neutral conditions in refluxing acetonitrile (equation 18).132... 

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