Cyclo-pentene

Hydrazine hydrate can often reduce vulnerable substituents on the pyrazolcme ring. One such example is the alkene group of the cyclopentenyl ring of pyrazol-3-one 16. It was found that heating 4-(l-methoxycarbonyl-2-oxopropyl)-2-cyclo-penten-l-ol 15 with hydrazine hydrate in ethanol afforded a mixture of pyrazol-3-one derivatives 16 and 17 in a 5 2 ratio (97JHC233) (Scheme 4). 

Dall Asta and Motroni (44, 57) provided direct experimental evidence for the transalkylidenation mechanism in the case of cycloalkenes. With a catalyst system consisting of WOCI4, C2H6A1C12, and benzoyl peroxide they prepared a random copolymer of cyclooctene and cyclopentene, the cyclo-pentene double bond being labeled with 14C. The distribution of the radioactivity in the copolymer formed will depend on the site of ring opening. 

Cydopantene-oxo-ozonidas. A monomer, C5Ha03, was prepd (Ref 2) by the ozonization of cyclo pentene dissolved in CC14. It is a yel, volatile liq with a penetrating odor sol in chlf, ethyl acetate and acetic acid is decompd explosively by coned sulfuric acid explds on heating... 

In the case above, 100 is protonated in the last step by the acid HA, but if the acid is omitted and a suitable nucleofuge is present, it may leave, resulting in a cyclo-pentene. In these cases the reagent is an allylic anion, but similar 3 + 2 cycloadditions involving allylic cations have also been reported. 

A tandem enzymatic aldol-intramolecular Homer-Wadsworth-Emmons reaction has been used in the synthesis of a cyclitol.310 The key steps are illustrated in Scheme 8.33. The phosphonate aldehyde was condensed with dihydroxyacetone phosphate (DHAP) in water with FDP aldolase to give the aldol adduct, which cyclizes with an intramolecular Horner-Wadsworth-Emmons reaction to give the cyclo-pentene product. The one-pot reaction takes place in aqueous solution at slightly acidic (pH 6.1-6.8) conditions. The aqueous Wittig-type reaction has also been investigated in DNA-templated synthesis.311... 

One important aspect of the photochemistry of aikenes 301,302) is the E—Z isomerization around the C—C double bond 303). This is also valid for cycloalkenes with the obvious exception of cyclopropenes304a,b) which exhibit a distinct photochemical behaviour, and cyclobutenes and cyclo-pentenes where the ring is to rigid to allow sufficient twisting of the double bond. 

The CpFe(C0)2 2 hy adduct exhibits no catalytic activity in the temperature range studied (200-300°C). However cyclo-pentene and cyclopentane are detected through GC monitoring of the gas-phase. A redox reaction Fe(0)/H+ is still occurring as for the Fe3(C0)12"HY adduct the evolved hydrogen allows the reduction of the cyclopentadienyl ligands. This behaviour already provides evidence for the location of the Fe(l) complexes within the large cavities of the zeolite. 

The energy differences seem to be somewhat unrealistic, specifically if one considers that 15, 16, and 17 can be regarded as analogues of trans-cyclo-pentene, /rani-cyclohexene, and respectively, as frans-cycloheptene.12 As has... 

If all the pentane is removed before pyrolysis, the bicyclo [2.1.0]pentane shows no impurities on vapor phase chromatography with a 20% Dow 710 on 50/60 U Anaprep column. Analysis by n.m.r. also revealed the absence of any traces of cyclo-pentene in the spectrum consisting of three complex multiplets at 0.3-0.8, 1.1-1.7, and 1.9-2.4 p.p.m. (downfield from internal tetramethylsilane reference). 

Substituted malonates and (5-keto-esters have also been successfully used as pronucleophiles (Scheme 9.11) [25a, 36]. From P-ketoesters, approximately 1 1 mixtures of epimers are generally formed. Products derived from 2-alkenylmalo-nates have been subjected to Ru-catalyzed ring-closing metathesis to give cyclo-pentene derivatives in good yield [25a, 36]. With the ester-amide displayed in Scheme 9.11 as pronucleophile, 1 1 mixtures of epimers were also formed [44]. 

Allyltrimethylsilane (la) reacts with cycloalkenes such as cyclohexene and cyclo-pentene at room temperature to give stereospecifically tra j -l-trimethylsilyl-2-al-lylcycloalkanes. These products are formed through trans addition and an allylic inversion. 

Cycloalkenes undergo ring-opening polymerization in the presence of coordination initiators based on transition metals to yield polymers containing a double bond, for instance, cyclo-pentene yields polypentenamer [IUPAC poly(pent-l-ene-l,5-diyl)] [Amass, 1989 Cazalis et al., 2000, 2002a,b Claverie and Soula, 2003 Doherty et al., 1986 Ivin, 1984, 1987 Ivin and Mol, 1997 Ofstead, 1988 Schrock, 1990, 1994 Tmka and Gmbbs, 2001], The... 

Zugabe des Substrats unter Kiihlung dann RiickfluB, 15b 3-(2-Amino-ethyl)-cyclo- penten 65 2... 

Reactions of pcrfluoroalkadienes with antimony(V) fluoride are similar to those of per-fluoroalkenes. Terminal dienes 1 rearrange with antimony(V) fluoride at 0-20 C selectively to internal dienes 2, in which the terminal trifluoromethyl groups are predominantly in the configuration.3,37,38 Higher temperatures and a threefold excess of catalyst lead to cyclo-pentenes (see Section 5.3.3.1.). 

Competing [ 4 + 2] and [ 2 + 2] photoadditions of a different type have been reported in the steroidal enedione (436), which on irradiation in cyclo-pentene, is converted to thedihydropyran (437) and the cyclobutane (438).382... 

We have already mentioned that it is the cis isomer of the 2,5-hexadienoyl halide which in the presence of nickel carbonyl cyclizes to give a cyclo-pentene derivative. The trans form reacts with acetylene to give (XXXV)... 

Three compounds appear to be of particular importance in flavor volatiles identified by Ching (3) from beef diffusate or dried beef. These are 2-hydroxy-3-methyl-2-cyclo-penten-l-one, 4-hydroxy-5-methyl-3(2H)-furanone and 4-mercapto-5-methyl-tetrahydro-3-furanone. 

Analogous bifunctionalizations of cyclohexene, 1-phenyl-2-butene and cyclo-pentene to l-halo-2-acetamido (acetoxy) adducts are reported by Weinberg and... 

Polymers produced at high catalyst concentrations have low molecular weights, consistent with melting over a broad temperature range (150-350°C). At low catalyst concentrations, crystalline polymers (which do not melt even at temperatures as high as about 400° C) may be produced if the catalyst is a chiral metallocene. Another important property of a polymer is the glass transition temperature, which is the temperature at which the polymer becomes flexible. The glass transition temperature of poly(cyclo-pentene) is about 65°C. 

This section is concerned only with the thermal rearrangements of 1-trimethyl-siloxy, 1-alkoxy-, 1-phenylthio- and 1-trimethylsilylvinylcyclopropanes into cyclo-pentene derivatives, which occurred either on heating in the liquid phase (sealed tube) at about 300 °C for 30 min, or by passing through a conditioned hot tube at 300 °C with a contact time of 4 sec or by flash thermolysis at 600 °C for 10 m sec3). 

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