Cyclopentenes, from

An illustrative example for the generation of cyclopentenes from vinylcyclopropanes is the formation of bicyclo[3.3.0]oct-l-ene 10 from 1,1-dicyclopropylethene 9 by two consecutive vinylcyclopropane cyclopentene rearrangements. ... 

Dichloro-1 -phenyl-3-methy I-1-phospha-3-cyclopentene from isoprene and dichlorophenyl-phosphine, 43, 73... 

Silvergerg SE, Lattner JR, Sanchez LE. Use of hydrogenative catalytic distillation to produce cyclopentane and/or cyclopentene from dicyclopentadiene. WO 0029358, Exxon Chemical Patents Inc., 2000. 

Show how you would prepare cyclopentene from each compound. 

We consider this reaction to be calorimetrically useful, especially given the interest in CpsUX derivatives by the thermochemical community . Like its Th analog, the reaction of Cp 2UMc2 with CO quantitatively yields dimeric 27, a Z-enediolate with a 10-membered ring. We may then ask about the enthalpies of interconversion with the respective monomer, noting that Zr and Hf form the monomeric 2-metala-l,3-dioxolenes, 27 167 j jjg corresponding carbocycles are (Z,Z)-l,6-cyclodecadiene and cyclopentene. From the enthalpy of hydrogenation of the former species and the enthalpies of formation of their saturated cycloalkane products , the conversion of 1,6-cyclodecadiene to two cyclopentenes is found to be endothermic by some 30 kJmol . 

Symmetrical secondary or tertiary alicyclic alcohols are readily dehydrated to only one olefin in each case. Examples include cyclopentene from cyclopentanol and phosphoric acid, cyclohexene from cyclohex-anol over alumina," cycloheptene from cycloheptanol and /6-naphthalene-... 

Dehydration of cyanohydrins to a, /3-olefinic nitriles has been accomplished by thionyl chloride, phosphorus pentoxide, or anhydrous potassium carbonate. A typical example is the preparation of 1-cyano-1-cyclopentene from cyclopentanone cyanohydrin (75%). Aluminum powder is the best of many catalysts studied for the dehydration of ethylene cyanohydrin to acrylonitrile, HjC=CHCN (80%). ... 

So far the di-ir-methane photoisomerization has found few applications in synthesis, despite the fact that vinylcyclopropanes are versatile intermediates. Several reviews discuss Aese compounds from a general point of view. For example, vinylcyclopropanes are prone to rearrange to cyclopentenes. Hence, in sequence, these two rearrangements may serve as a way to produce cyclopentenes from 1,4-dienes. ... 

Danheiser cyclopentene annulation Formation of cyclopentenes from enones and allenes. 124... 

The nonKolbe electrolysis of carboxylic acids can be used for a selective fragmentation, when the car-bocation formed initially is stabilized in the -y-position by a hydroxy or trimethylsilyl group. This way the reaction can be used for a four-carbon ring extension (Table 12, entries 1 and 2). Furthermore it can be applied for the stereospiecific construction of cis- or rraru-disubstituted cyclopentenes from 6-hydroxynorbomane-2-carboxylic acids (Table 12, entries 3 and 4). 

Scheme 25) was observed when cyclic alkenes (e.g., 214) were treated with ruthenium carbene complex 18 in the presence of terminal alkynes (e.g., 215). A mechanism involving initial ROM, followed by alkyne insertion of the intermediate carbene complex, followed by ROM from intermediate 217, was proposed. In order to account for the unexpectedly high yield (the yield is higher than the anticipated E Z selectivity in the formation of 217) of the process, a second source of the observed product involving metathesis of an additional mole of cyclopentene from intermediate 217 was suggested. 

Outline a synthesis of cyclopentene from each of the following ... 

The PKR was first reported as a stoichiometric reaction between norbomadiene and a complex of acetylene bound to hexacarbonyl dicobalt (Equation 17.72). Pauson and coworkers also reported the first catalytic intermolecular formation of a cyclopentene from an alkyne, an olefin, and CO (Equation 17.73). The first intramolecular version of the PKR was reported almost 10 years later by Shore (Equation 17.74). At this point, the intramolecular PKR has been studied in more detail than the intermolecular PKR. 

The reaction mechanism is discussed kinetically for the formation of cyclopentene from an allyl radical and ethylene. 

Yudha, S., Kuninobu, Y, Takai, K. (2008). Rhenium-catalyzed synthesis of stereodefined cyclopentenes from b-ketoesters and aliphatic allenes. Angewandte Chemie International Edition, 47, 9318-9321. 

---