Cyclopentadienone synthesis

Casey CP, Guan H (2009) Cyclopentadienone iron alcohol complexes synthesis, reactivity, and implications for the mechanism of iron-catalyzed hydrogenation of aldehydes. J Am Chem Soc 131 2499-2507... 

The ring system can be generated by D-A addition of a substituted cyclopentadienone and an alkyne. A reaction sequence involving addition followed by CO elimination can be used for the synthesis of highly substituted benzene rings.308... 

A more complex reaction is involved in the cooligomerization of acetylenes and tert-butyl isocyanide using nickel acetate as the catalyst (Scheme 20)43 the nature of intermediate complexes leading to the formation of 2-cyano-5-terf-butylaminopyrroles has not been established. Cocyclization of tert-butyl isocyanide with coordinated hexafluoro-2-butyne gives rise to coordinated cyclopentadienone anils for molybdenum systems,44 hence the nature of acetylene substitutents and of the organometallic catalyst play crucial roles in these processes. The pyrrole products from the former reaction can be decomposed by sulfuric acid and the overall sequence provides a simple synthesis of 5-amino-2-cyanopyrroles (Scheme 20). 

Common error alert Many cume points have been lost over the years when graduate students used cyclohexadienone or cyclopentadienone as a starting material in a synthesis problem ]... 

A rather novel application of the Diels-Alder reaction is the synthesis of dendrimers. Mullen and coworkers116 made cyclopentadienone 161 react with SA AA -tetraethynylbi-phenyl 162. This afforded, after extrusion of carbon monoxide, a first generation dendrimer 163 containing 22 phenyl rings (equation 45). Cyclopentadienone 161 reacted only as a diene, since the bulky triisopropyl groups prevented the ethynyl functions from reacting. 

It has been established that the course of the sequential pericyclic reaction of cyclopentadienones with acyclic conjugated alkadienes depends on the reaction temperature, thermal treatment at low temperatures affording 3a,4,7,7a-tetrahydroinden-l-one derivatives by way of a Cope rearrangement (see Scheme 38). Roman et al have developed an efficient stereoselective synthesis of enantiomerically pure i-nitrotricyclo[5.2.2.0 ]undeca-3,8-dienes via a tandem consecutive asymmetric Diels-Alder-Cope rearrangement (see Scheme 39). Adducts... 

Vaska s complex ([IrCl(CO)(PPh3)2]) also catalyzed the carbonylative coupling of diynes, which provided bicyclic cyclopentadienones (Scheme 11.23) [35]. Due to the instability of the products, the substrates are limited to symmetrical diynes with aromatic groups on their termini nonetheless, this reaction still serves as the catalytic and practical procedure for the synthesis of cyclopentadienones, which are anti-aromatic with a 47t system and serve as active synthetic intermediates. 

As was mentioned in Section III,A a very useful method of synthesis of olefin complexes involves the displacement of carbon monoxide from metal carbonyls by olefins. Under similar conditions acetylenes usually react to give new ligands, e.g., cyclobutadienes, cyclopentadienones, and quinones (see Sections V,E and VI,C), and it is not surprising, therefore, that the range of known acetylene complexes is smaller than the range of olefin complexes. 

A further method for the synthesis of o-diaroylbenzenes has been described by Ried and Bdnninghausen. Tetracyclone (145), a potent diene for Diels-Alder reactions, together with dibenzoylacetylene (146) gives 147. This method has proved of value in a number of other cases and is also applicable when the cyclopentadienone derivative is dimeric ° as in the case of 2,5-dialkyl-3,4-diarylcyclopentadienones. °... 

Cyclopentadienones.2 Cyclopentadienones are generally not useful synthons because of their ready dimerization. A new synthesis of more stable substituted cyclopentadienones involves cyclization of two substituted alkynes with carbon monoxide by the [2 + 2 + 21cycloadditions shown in equations (I) and (II). 

The iron-mediated [2 + 2 + 1]-cycloaddition to cyclopentadienones has been successfully applied to the synthesis of corannulene [24] and the yohimbane alkaloid ( )-demethoxycarbonyldihydrogambirtannine [25]. A [2 + 2 + l]-cydoaddition of an alkene, an alkyne and carbon monoxide mediated by pentacarbonyliron, related to the well-known Pauson-Khand reaction [26], has also been described to afford cyclopentenones [27]. 

SCS-MP2 and the new perturbative B2-PLYP density functional methods provide accurate reaction barriers and outperform MP2 and B3-LYP methods when applied to the 1,3-dipolar cycloaddition reactions of ethylene and acetylene.39 Phosphepine has been shown to catalyse the asymmetric 3 + 2-cycloaddition of allenes with a variety of enones (e.g. chalcones) to produce highly functionalized cyclopentenes with good enantiomeric excess.40 The AuPPh3SbF6 complex catalysed the intramolecular 3 + 2- cycloaddition of unactivated arenyne- (or enyne)-yne functionalities under ambient conditions.41 A review of the use of Rh(I)-catalysed 3 + 2-cycloadditions of diaryl-and arylalkyl-cyclopropenones and aryl-, heteroaryl-, and dialkyl-substituted alkynes to synthesise cyclopentadienones for use in the synthesis of natural products, polymers, dendrimers, and antigen-presenting scaffolds has been presented.42... 

Convergent synthesis (Fig. 4.18) also uses cyclopentadienone for construction of the dendrons. However, in this case two molecules of the diene are added via Diels-Alder reaction to 4,4 -diethynylbenzil. The resulting second-generation den-dron is reacted with dibenzylacetone in a twofold Knoevenagel reaction. The newly functionalised cyclopentadienone dendron obtained again undergoes (fourfold) Diels-Alder addition to the tetraethynylated tetraphenylmethane core unit [34a]. 

A number of examples exist involving reactions of CpCo(CO)2 and silylated alkynes. Cycloaddition of MesSiC CH gives a 3 1 mixture of 2,5- and 2,4-bis(trimethylsilyl)cyclopentadienone complexes. The use instead of [C5Me5]Co(CO)2 reverses the regioselectivity to 1 3.7, presumably due to the increased steric crowding about cobalt (equation 9). This effect has yet to be exploited in synthesis. 

Cyclopentadienone is an elusive compound that has been sought for many years but with little success. Molecular orbital calculations predict that it should be highly reactive, and so it is it exists only as the dimer. The tetraphenyl derivative of this compound is to be synthesized in this experiment. This derivative is stable, and reacts readily with dienophiles. It is used not only for the synthesis of highly aromatic, highly arylated compounds, but also for examination of the mechanism of the Diels-Alder reaction itself. Tetraphenylcyclopentadienone has been carefully studied by means of molecular orbital methods in attempts to understand its unusual reactivity, color, and dipole moment. In Chapter 48 this highly reactive molecule is used to trap the fleeting benzyne to form tetraphenylnaphthalene. Indeed, this reaction constitutes evidence that benzyne does exist. 

Synthesis of Cycloalkenedtones, Cyclopentenones, Cyclohexa-and Cyclopentadienones, Alkenes, and Dienes... 

Zhu, J., Klunder, A. J. H., Zwanenburg, B. Synthesis of 6-functionalized tricyclodecadienones using Barton s radical decarboxylation reaction. Generation of tricyclo[5.2.1.0 ]decatrienone, a norbornene annulated cyclopentadienone. Tetrahedron 1995, 51, 5099-5116. 

Ring-opening reactions of cyclopropylcarbene and -carbyne complexes have been used in the synthesis of open-chain products, cyclopentenones, cyclopentadienones, cyclohepta-... 

A facile synthesis of cyclopentadienone epoxides via thermal rDA cycloreversion of a tricyclodece-none epoxide and its acetal derivatives has been applied to the preparation of cyclopentanoid antibiotics. - This procedure has been used in an efficient synthesis of terrein, a mould metabolite from Aspergillus terreus, by rDA synthesis of cyclopentadiene epoxide intermediate (57). FVP conditions for these reactions typically involve temperatures of 420-600 C. Furan-derived DA adducts have also been used to generate cyclopentadienone epoxides. The thermal rDA reaction of the furan-derived DA adduct (58) proceeds at temperatures as low as 330 °C with complete cycloreversion and generation of epoxide (59) in nearly quantitative yield (equation 32). Subsequent elaboration led to epipentenomycin derivatives such as (60). 

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